CV4 was my first CV game. I played the hell out of it, and it was a long time before I ever tried another CV game. For that reason, and my fondness of the SNES, CV4 was always my favorite. The first CV games I tried after 4 were the NES ones, and they seemed archaic and dull compared to 4. And too hard.

But after time, they really grew on me. Speaking from nostalgia, it'd be a hard choice. CV4 would be a contender (but at this point in my life, I guess I can be nostalgic for CV1 and 3 as well). But as far as how much fun I have playing the games these days, I enjoy playing CV1 and 3 more than 4.
I've been itching to play Symphony of the Night again. I haven't played through that game in a few years now. I can't remember the last time I did. But now I'm stuck with which version to play. The original PS1 version, the Saturn version, the PSP version... And come to think of it, I haven't yet played the fan re-translated PS1 version (original Japanese voice acting but with translated text).