I know this is a common noob question, but I have been playing for a decent while and ready s6 to try to carry myself out of low elo. So basically 1v5 enemy team. I play vlad very well, but he is not mobile enough or high skillcap. I am looking for a high skill, mobile, mid or jungle, late game champion who is viable in low and mostly high elo. Any suggestions? I have been looking at Azir, Kha, Rengar, Ahri, Zed, Riven, LeBlanc. Just to give you an idea.
Rengar and Kha'Zix as your mains. Both are extremely fun and Rengar himself can be insanely versatile depending on how you build. I only do him Jungle for Assassin cause I suck ass at lane and building him bruiser with Cinderhulk and all the new Juggernaut items is insane. You can still burst people with this build and the standard combo: 
. And you also never die, quite literally because of your W's free stats and the Sterak's Gage + Skirm Smite. I have yet to try the AP build but I've watched NB3 do it and it's pretty damn insane. Think of it like having Viktor burst but as a suicide bomber.
Kha'Zix can't really do that much in terms of build variety but he's more Assassin-like than Rengar with his isolation mechanic and reset on evolved E. Rengar you just run in there with full build and 5 ferocity, do your combo, and a person is two is instantly dead unless you get spotted through stealth with a pink or something. Once you get evolved Q on bug boy and you 1v1 an isolated target, you should automatically win every time because the base and scaling is really fucking amazing. The higher you're champ level is the more base your evolved Q has with isolation damage.
Here's my build on Assassin Kha'Zix Jungle: 
. I guess with the Deadman's Plate it's sort of bruiser, but a lot of people get something like 
or 
for their last item anyway because of how vulnerable you are in late game team fights. You can also throw in somewhere in there but I can't rely on the armour shred so much because LW gives the same amount at full stacks but immediately on damage. The only way i see BC as useful is if I'm going for some poke build because of how you can apply stacks on multiple targets until you can go in. That's why I normally replace BC with in the assassin build because it gives the phage passive but the sheen proc + your own passive is such amazing damage. Also, all of the stats benefit Kha in one way or another. And since your Q is like a 2.5 sec-ish CD at 40% CDR (it's 3.5 at all ranks), you can re-apply the sheen insanely quick.
The Hydra active is also available while in mid-leap and makes your E do a lot more damage since Riot gutted the scaling. So make sure to Hydra/Tiamat mid-air for maximum damage as you land. Same thing with Rengar in his 5 Fero burst combo. As a Jungle main, I don't really have much to offer in terms of how they both do in Top, but go look up Ryan Choi and some Kha'Zix top high elo games for info. I also used to know Damir who is the best Kha'Zix player in NA, and he taught me a lot with Jungle Kha.
Other than that man, just main what you want. Experiment with all of those champions in their best roles and find what flies with you. Best of luck from the Epimemer. 
Whoever you feel like playing, if you gotta try all the champs, do it, JUST DO IT.
Katarina
Riven is brainlessly easy and extremely overpowered.
Snowballs very hard and very hard to gank. Pick Riven.
I literally spammed LeBlanc for 2 weeks and went from Silver 5 to Gold 5, i recommend you to play LeBlanc as well
zyra jungle is my jungle main for a LONG time, her burst is amazing and with a lock down, knock up, and 3 auto attacks at once she is one of my favorite jugnlers, the only thing that you need to watch out for is gap closers. you tank the small monsters and your plant tanks the big one
zyra mid lane is great too with amazing late game scaling.
yasuo is a champion i love, and is overloaded with gap closers out my ass hole, double crit, damage shield passive, projectile shield, spammable q, no recorses to hold you back, a knock up, and something to keep them knocked up for longer(ult)
fiora was played a lot in lcs and is op, but i never play her. ult the lowest one in a team fight and everyone dives that person, then you have a 4v5 with a heal in your favor.
thresh is my main support, he is fun and is an amazing tank that can peel like hell.
Ahri is the easiest out of the champions you mentioned.
LeBlanc is my favourite.
I would not suggest going for Azir or Riven, at least in rankeds, until you really get the hang of it.
