I main top in ranked, I usually duo with a friend and I usually peel for him while he picks up kills like a 
and I like to peel while also doing a lot of damage like Volibear 
(yes it still works and extremely strong)
But sometimes the opposing team do have strong Volibear counters, but I prefer being able to take a lot of damage but also dealing it.
Who'd be best for the job? Renekton, Rumble, or Vladmir?
Renekton. But hey, it's a matter of personal preference
non of them is a good peeler. Renekton is a lanebully and later on good for diveing/zoneing carrys, Rumble is a aoe monster with incredible midgame teamfights, Vlad scales into a immortal god of death in the lategame, but nin of them really got good tools for peeling.
Darius could work, he can pull guys away form you carrys slow them down, and thx to truedamage ult and free %pen, he can easily be a threat for enemie tanks and thus help you carrys killing the frontline. And just like volly, he got problems reaching the backline, but if he does, he hurts alot on the other hand, he is probably to similyr to voli and gets kinda countered by the dame things.
Lulu is great at peeling, got definitly not the same counters as voli, and can do quite some damage, If you want to hount kills like a Nida, Jayce is somewhat similar, a but more risky but also with more damage potential as NIda.
