Oh my god, AP Tristana is so hilarious
Her AP to flat damage ratio is better than Veigar's, I think. This means that I can get up to 1200 damage in one attack with ease, and coupling that with rocket jump reigns terror on
bots D:
Veigar is also capable of getting 1.3 AP per kill with Q and 6.5 AP per champ kill, 7.8 AP if you kill them with Q. (assuming you have a deathcap, which you should have one)
and then there's his super cool item deathfire grasp.
oh and his ult isn't only 1.2x, it's also 0.8x enemy AP
AP trist falls flat on her face late game. I've seen someone try to play her, thought they were 'beasting the game and that i'm stupid for thinking AP trist fails', and then started dying no matter what they did.