I've got four I really loved, flaws and all.
First two were part of my series,
Pokemon Odyssey 1 and
Pokemon Odyssey: A New Beginning. Odyssey 1 was my first RP I ever GMed, and one of the first RPs I ever was apart of. I didn't really know what I was doing in the beginning, so it was kinda a mess to get used to RPing and GMing. Once I did, it was a great ride all the way to the end.
Odyssey 3 was much better in terms of writing and story. It was longer, had overall a better cast, and I believe was a much stronger RP. It also had so many moments that the RPers helped create that I can always come back to and think about, and say, "That was amazing."
The next one is
Aerion. This was the most ambitious RP I have ever done. With Raikiri, we made this high fantasy RP in a world we created called Aerion. It lasted a few months, but it was packed with memorable moments and dialogue. I don't think I've ever seen better writing in a roleplay than in Aerion. Posts were always top notch, which meant I also had to step it up. It is one of my favorite roleplays I've ever been apart of.
This next one is an interesting choice:
La storia della Arcana Famiglia. It was a great roleplay to be apart of simply for the character interaction we created. I joined this as a group with a few of my roleplaying buddies, and it was glorious. It didn't last nearly as long as I would have liked, but I always enjoy looking back on it.