First one. Don't remember much of the other 2 PS1 games. Spyro had impressive draw distance for PS1.

Ripto's Rage (or Gateway to Glimmer as it was known here). The only one I've played through multiple times.

It also had pretty good voice actors, as well. If I remember correctly, the guy who would soon go on to voice Spongebob even worked on one of the titles lol.

Spyro Year of the Dragon was always my favorite due to having the best worlds, gem finding, and minigames.

I'll be honest

I quite enjoyed dawn of the dragon (on home consoles)
I also liked shadow legacy on the DS

The OG has a certain charm the subsequent entries didn't imo. Though Ripto's Rage and Year of the Dragon are still very good.

Are these games even popular altogether?

The first game is my favorite. I just prefer the level design and the flow of gameplay. I found it more engaging than the other games. I must've replayed that game hundreds of times as a kid. The other two from the original trilogy are great as well.