So I'm level 15 and am getting close to 4800 ip and want to get a tank toplane most likely renek or darius. So which one is better and why? Thank you. Also vote on the poll. 
or 
. Ahh it's a tough decision. So please help. Thanks in Advance. And for which champ you think is better, please provide some tips and tricks.
Technically, neither Renekton nor Darius is a tank. They should both build Black Cleaver and a mix of damage and tankiness. If you want a true tank, you shouldn't play either of them. You should instead play someone like Poppy or Sion.
But I'm guessing that you know you want to play either Renekton or Darius, and you just want help picking between them. They each have advantages and disadvantages. Here's a comparison.
Renekton is more mobile and burstier. This makes him better for jumping onto squishy people and destroying them, which in turn makes roaming to the lanes where the squishy people are fun.
Darius counters tanks mostly, but has no bad melee match-ups. The longer the fight goes, the more likely he is to get 5 bleed stacks on an enemy, and that is when Darius becomes much more dangerous. He has more in-combat sustain than Renekton if he can hit champions with the blade part of his Q, which makes his teamfighting in general a little bit easier. You just need to get to 5 bleed stacks on someone, and then you can get to 5 bleed stacks on anyone and start pressing R.
I prefer to play Renekton, but I'm going to recommend that you play Darius. Easier teamfighting is pretty big in low elo. (Of course, in low elo, the squishies aren't likely to position themselves very well, which makes Renekton easier to play, too.)
Some tips and tricks for Darius: If you press W immediately after auto-attacking, you can auto-attack again immediately. This helps you deal more damage and makes the enemy bleed more, so it's useful. Remember that his Q only heals him if it catches an enemy champion in the blade part of the circle. If an enemy doesn't have a dash available, slowing them with W and then walking away from them (if they're walking towards you) or towards them (if they're walking away from you) while casting Q will almost always hit them with the blade part of the Q. You can make many enemies back off by casting Q or by threatening to pull them in with E. Prioritize leveling your abilities in this order: R>Q>E>W, but have one point in each basic ability by level 3. Your general fighting pattern is to pull people in with E (but if they dash in on you, don't waste it; wait to use it to stop them from running away), attack them, then slow them with W, and then hit them with Q. Keep hitting them with auto-attacks and Q's until they're low enough, and then ult them for the kill.
And some tips and tricks for Renekton, just in case: Remember that your Q heals you when it hits minions and heals you even more if you hit enemy champions. It also heals more if you have 50 or more Fury when you use it. When Renekton uses his E to dash, he can dash again if he hit an enemy with the first dash. Try to hit enemies with the first dash so that you can dash again, to better escape or chase. Also, you can dash in and out of a fight. Dashing in with E, attacking an enemy, stunning them with W, and then slicing them with Q before dashing out again with your second E is a general fighting pattern for Renekton. If you want to dash in and out, don't mash E. Renekton recently got some improvements to make playing him smoother. Now when he's in the middle of a dash, the game doesn't forget other buttons pressed. If you press E while dashing, his second dash will be used immediately after the first dash ends. This can make you accidentally double-dash before you get used to it, and if you accidentally double-dash in, you can't dash out. Prioritize leveling your abilities in this order: R>Q>E>W, but have one point in each basic ability by level 3.
Darius and buy DunkMaster. It increases your dmg by 1337%.
darius is actually fun to play
so pick him
renekton is fun
Darius is easier in my opinion, but neither are "tanks"
good luck and welcome to the top lane, the best lane.
Darius has some bullshit damage however lacks mobiltiy. Renekton has a stable heals while darius has a %missing hp heal. Darius lacks mobility but has true damage and that ult. Renekton is more stable and easier in my opinion
