Zed gets a better rep thanks to reliablility. He can duel damn near anything and split push with total impunity. Essentially, he has a job outside of killing somebody and blowing up after. Talon will realistically not escape after a kill, as somebody will have oracles for his ult, and if that is a support than he has to leave the adc alive to remove it. He's still a powerful champion, but he is more of a one-trick pony than the other assassins that are popular. Fizz can escape and continue slaughtering in 6 seconds or less, Zed WILL escape (and can be a pain in the ass to kill), and Kassadin is Kassadin. The one thing that keeps Talon underrated is his suicidal tendency. He can be stopped with skill by a different enemy, and any halfway intelligent ADC will never come near his E range. After that, what can he do? Go assault a bruiser? Ult and pray nobody nearby has oracle to catch him en route, THEN pray he has enough damage without R for the kill?
@Baylee: I actually used to play Talon with Triforce, I have no idea why the last buff didn't bring that back to mind, I need to do some math and see if that adds anything. Although I'm not sure why you would use gunblade. Seeing Talon as he is, a suicide champ, the spellvamp feels rather useless. Same for Botrk, AS is not too core on a burster. If I am playing anything full suicide, I go all the way. As in, brutalizer -> BT -> LW -> BTx4 (with arpen reds/quints to get the most of it). He loses out on some gimmicks, but his combo makes Veigar jealous for raw damage - at the given 5.8 bonus AD scaling, 600 bonus AD, and 850 base, that's well over 4k damage. (a numbers comparison between he and Zed means nothing when one builds 200+ AD more than the other).