PS1: From memory, Spyro. I never played it from start to finish but I remember liking it. (Need to buy it off PSN and play it properly.) Have tried Crash 1 & 3 recently and didn't really like it. MediEvil is still in my "need to play" pile.
PS2: Ratchet, no question. My favourite game series. Sly in second place, Jak a distant third - have always found the gameplay rather frustrating. (Can't judge on story, never got far into 2, started 3 but it seemed like I'd missed too much.)
PS3: Uncharted is the only one I've played-and-liked. I tried Resistance but didn't get far into it - not my sort of game, and I just really dislike first-person view. It always seems uncomfortably close and tunnel-vision-y.