What really attracted me to Crash was that Sonic took a few extra years to move into 3D, and Crash did a good job at taking the style and kind of putting it in 3D before Adventure came along. They're definitely some of the highest quality games on the system, and really, playing Crash and Spyro has spoiled me for PS1 games, given that they look and play so much better than the average game on the system.
And while I had both an SNES and a Genesis, I had a PS1 over an N64. Honestly, going back and playing both now, the N64 still feels so technologically inferior to the PS1 that, even though there are still a few games that are just great, it still pales in comparison in so many ways. I don't get the hype for Ocarina of Time, even though I love Zelda overall (Link to the Past 4 lyfe), when I look and see that it came out the same year as games that had such better graphics, music, and the like on the competing system (like Spyro 1, which is somewhat similar in many respects).
Kirby is pretty neat. I have to admit it has a great style, but given the choice between a Kirby and a Mario game, which is frequently what it would come down to for me, I'd have to go with Mario, given that his games are always absolutely top notch.