I personally play Conduit 2 a lot more but there is no question that the Metroid Prime series is far superior, so that's where my vote has to go. I also did quite like the splitscreen on Echoes. Perhaps in the event of a fourth there would be online.
Conduit 2 doesn't stand a chance. All three Prime games are awesome, but i think the first one is the best. I've passed it at least 10 times already and i still can't get it to 100% on my own.
This. Except I can never 100% Prime 2. I always miss a scan somewhere. I gave up trying. Got the others though. Never once used a guide either. Just always miss a dang scan. Just one. Every time I play Prime 2.
Plus it's 3 games to one. 3 great games to one. No contest.