Metal Gear Solid vs. Splinter Cell

So we had a nice long argument in /v/ discussing both of these games, it went on longer than expected with both sides showing lots of support. Let's try to continue the discussion here: What series is better? but most importantly, why is it better?

A game can be technically better, have a better story or better gameplay. I can safely say that Forza Motosport is better than Big Rigs: Over the road racing, and it would be correct.