MGS3 is not only technically the more impressive game, but IMO looks better too (yes, I've played and completed both games).
Resident Evil probably has the edge in image quality and clarity in stills, but when you're playing, you just start to notice how much more interactive everything is in MGS3. Not only that, but the whole setting is more varied as well - from lakes to the forrest to the more industrial setting in the later levels.