I only like the first MGS on the original PlayStation, one of the best games of all time. The second game was an overblown mess with very lame characters and a story I still don't understand, it is one of the worst movies I have ever seen. MGS4 was basically like MGS2 on steroids, and I didn't care for it. Snake Eater was really good but I never finished it, I think it was a lot better than 2 or 4 though. The only Splinter Cell game I didn't like was Double Agent, although Pandora Tomorrow had horrible voice acting and music.
I will go with the Splinter Cell games on this one, they feel more like real stealth games and I prefer the gameplay. I think MGS started out great but the sequels were too ridiculous for their own good, and I think that the gameplay could still use some work.
Edit: I didn't vote in the poll or mention the new SC because I haven't played it yet.
Essay Pro