Hi there,
Ardent Censer and the support enchanters was extremly powerful last season or maybe 2 seasons ago I should say, now they are very weak in comparison. This is important to know becouse alot of discussions and about the subject is still affected by this fact so be careful becouse many players still talks about this old game state in anger and might not always be fair and true to facts.
Again no right choices but all the items you are able to buy is put into the game for its own little reason so.
This is a question about identifying the right situation rather than buying the most "op" item.
So I will give you a personal preference and reasoning when it comes to items:
I do not often hang out in the backline as Janna, I prefer to move around alot and ward and be in the fight, many times I love tanky stats to allow me the freedom to move around in a teamfight and atleast take a few hits without dying this also makes it alot easier to get into somones face fast to interuppt something for example a channeled high dmg ult like Miss fortune or velkoz.
This being said I value tanky stats high but I do not build full tank either.
I buy Ardent Censer if I have an adc that scales really well with attack speed... for example Vayne, cait, Jinx or Ashe or if I have a very snowballed Yasuo in a lane or something like that. You will help them to carry you so find who on the map you think is best equipped to do so and play around that.
However the only time I personally would find it to be a bad thing to buy this item is if your team is very ap heavy in which case I dont think I would have picked Janna anyway.
She loves this item becouse her E gives ad to combine that steroid with AS can be very very strong. So certain items can have different impact on different supports.
I buy Redemption when enemy team has strong aoe or ardent censer is not a good option sometimes I build it anyway becouse why not? you can potentially get a heal off for your whole team so it is not a bad item + it gives you slightly higher hp which is something I would value very high unless I can dodge like everything which isnt human so. Redemption is not very effective against very high burst however since that would mean you have to pre cast redemtion before the nuke which yeah isnt always that easy to pull off.
In the case of assasins and high burst.. im still struggling here myself but
can be helpful and it is also a good item against heavy aoe champions and strong aoe ults.
You do not have to buy any of those items in any of your games if you do not want to. Many AP items or tanky items can benefit you and your team in the long run so play around.
Personally I like almost all of the support items atleast when it comes to how they work or their purpose.(meaning the balancing of them are not always something that makes me smile if I put it like that)
"AND.... One of the biggest questions, which enemy sups can I win against in lane,?"
This is an impossible question to answer with exactly what champions you can beat.
Becouse if you calculate the math between 2 champions it will not give you a result of who would win just who would from a math point but that doesnt calculate people going back to refill hp or dodging skill shots and the other 8 players in the game who could tilt that balance in any direction.
Every single one of them my friend. It is just a matter of choices, experience and what mistakes the enemy does and you do that game.
In bot lane you are also a part of a duo so your ad and enemy ad plays in alot.
I mean lets say you have a really good ad player with you... many times the only thing I have to do is to apply some cc or to show my ad that Im ready to back him or her up for that person to engage and get kills.
One thing to remember also is that you do not always or have to or even want to pick supports with kill pressure in lane. Janna is a very passive support with (in a good old "balanced" lol game" very low kill pressure atleast on her own.
I know the Janna and Cait combo can be very hard even though it doesnt seem or even should be so but Its a poke lane and while sure the lane itself can often be rather easy for the Janna player... Cait will fall of during a long period in the game. Outside of lane this lane needs cait to have 4-6 items to be competitive and strong which is a hard point to get to especially if you are a beginner since the farm or cs is generally really low.
Junglers and roams can also really tilt the balance in bot especially since it usually means multikills and not a solo kill like in the solo lanes.
To answer your question about Fiddle... first he is not actually a support atleast that is not how he was released.
So I personally hope that this is not a question you should even have to learn about but in case that isnt the case.
Here is how I would try to beat Fiddle in lane even though I personally have a whole list of more threatning champions to face in lane... 1 you do not pick Janna into him and if you did you want an ad with high burst almost solo kill pressure.
I can´t imagine fiddle to be a common issue in botlane but if I was a new player I would pull my hair out in anger over laning against that poke spam.
Max shield and try to position yourself so he cant bounce his e so much. Be respectuful against his lvl6 and keep wards up in bushes as much as possible to counter suprise ults. Ask your jungler nicely to gank, be aweare that a gank could potentially backfire really hard if he can bounce his e on 2 targets.
Some lanes are just a nightmare and a matter of killing time and trying to survive until bot starts to move and group with the team.
It is just how it is.
Lets say I knew I was up against a Fiddle... I would pick Nautilus I think just q his face he will burn his cd:s on your shield and your ad can follow up with damage. This is probably the hardest choice that I will recommend becouse this makes you a frontliner which is as far from our role I could think of.
It also forces you to go in and trade among minions which is one the biggest "beginner killers" in lane I could imagine.
Nautilus is just an easier to play Thresh basically, Nautilus´s hook is also alot harder to dodge.
But this is something I would have tried atleast.
Nami is a nice and easy pick... if you prefer to sustain through the poke, sona and soraka could potentially also find success here but raka would eat her own health to keep the ad high or topped so can´t say how it would play out potentially even worse than Janna.
The final recomendation is to fight fire with fire. If the enemy support goes damage bursts and poke... you pick something with even more burst or poke! :)
Zyras plants can eat alot of the annoying e bounces and tank for you so that is a decent pick I recon can also interuppt his channeling.
Or just some mage with high poke or burst xerath or brand could work... maybe annie can potentially flash tibbers delete him.
In synergy with Janna I love to play together with Draven becouse I have a friend that plays him alot and that is one of few lanes that often lands kills when I play Janna so that is always fun... if that is not an option Im equally fine with just safe farming the lane out.
Janna has very helpful tools to both damage and durability but sometimes all you can do is to give that shield and hope your ad also identified the kill window and went for it, when that backfires it very important to back out immediately... try to get a dialog or teamwork going with someone who wants to go in and trade with shield and then back out... or to stay on target becouse you would kill them. Keep repeating this to make most use of Janna. Go in trade with shield, fall back and then repeat.
(Can mention here that Draven/Nami is one of the most disgusting lanes I have ever tried... land a Q with a good draven player in your team and watch him go to town xD)
You mentioned Cait... Janna can do great things for her but I honestly prefer to rather pick something that could engage or peel more physically for Cait than Janna.. becouse Cait has a long and slow scale curve mid game where she is rather weak and I prefer to pick something that allows her to get there rather than something that makes her even stronger once she actually gets there and with Janna Im very bound to make plays on other plays especially if our comp is rather poke:ish which both Janna and Cait are, so its easier to play something else here for me. Cait has very long range and also has own escape tools so shielding her just to buff her in a a teamfight is not always optimal and "lost" us a cencer procc for Cait which instantly made her less potent and therefore also Jannas impact on the game. This is what I have reflected over in my Janna / Cait games atleast.
Janna / Yasuo bot is so much fun + it often makes Yasuo players happy when they get to do that so if you havent yet tried it.. I recommend it :)
Ad steroid from E is what she does or ad + as with ardent cencer so the more a champion benefit from those stats the better Janna will perform aswell but at the same time you can also use the shield only as a survival tool which still makes Janna good and viable.
You can also play Janna only as a simple distruption tool if the enemy have many champions that wishes to dive into your team... you can knock them up or knock them away with ult.
Janna is not really bad with anyone I mean she is more optimal with some but you can play her in combo with almost anything and into almost anything so as a champion she fits the role she has very well much more than some other supports Imo but everything is viable especially when you play with beginners the higher your skill becomes the more and more important small details in the game will matter but for now just enjoy learning, experimenting and have fun.
Turned into another wall but I said I could talk about Janna and supporting forever so xD