As for "Best" with last hitting, Vlad, Morde and champs with free AoE spams are pretty good at farming usually, but I wouldnt play a champ just because they can last hit well, unless you enjoy playing them. I can hit 200+ creeps in 20 min on Vi, using her E's correctly. But as stated above, you have to know your champs. Often time's ill see people going back with full mana. If you dont plan on popping all ur mana harassing, use it to last hit better.(But save some in the case a fight breaks out or for escapes) For example jax's W resets auto attacks in the case you do miss, or it deals extra damage to last hit better under a turrent. You just have to focus and know pretty much exactly how much damage you deal, and try and hit it right when that damage will get the last hit. Hope I helped!