Who is the best spilt pusher?
that ^
that ^

Quinn: Has the best mobility for constant rotations, and can do good damage to towers. The safest split pusher, since her mobility will allow her to escape even 5 man collapses if warded properly.
Zed: Has the best 100-0 ability to snag the ADC that went to solo clear a big wave, then use that wave to split push down a tower.
Udyr: Probably has the best combined tower destroying power with survivability. He can survive a long time 1v3 to even 1v5. Long enough for your team to take Baron if the enemy tries to take him down with too many resources. (i.e. the best bait split pusher in my opinion).
Tryndamere: Gets 6 extra seconds to take down the tower - the best splitpusher for taking inhibs basically, as it's typically worth trading the death for the inhib and his ult lets him finish what he's started.
Kayle: Like Tryndamere, although the ultimate isn't as strong. Being ranged may be worth something I guess.
Best? Debatable. Probably
or
.
Most fun? 
if ur team will let u
<3
<3
Ezreal doesn't even need to be in lane to clear out the minion waves :)
Nasus...at 300 stacks it only takes a few SEC's...at 700+ the enemy just kills your whole team THEN worries about you.