I like them both. I think the gameplay is equal in my opinion. Double Agent was the only SC game that I never played.

Not played Conviction yet so obviously can't say.

I thought MGS4 was very overrated. I am not a huge stealth games fan (except for Thief and Hitman series) but did like some of the older SC games.

I'm going with Splinter Cell on this one. Not to judge the new game Conviction, but the series as a whole, i even loved Double Agent, and played through multiple times. I think the SC series has always evolved sleath, and the use of shadows/hiding, while Metal Gear has remained unchanged. I shouldn't be able to pop a box out of nowhere and hide from a solider in MSG4...not anymore, that was for back in the day (and yes i have MGS4, and know the soliders can lift the box...but that's still more of the same).

Shooting out a light, using a EMP, or cutting the main line for a generator to cause chaos, and infiltrate a base however...that's sleath, and that's innovation. I've played through MGS4 about 4-5 times now with different playing styles to unlock different perks on my next playthrough, but on my last playthough it took like 5 hours to beat the whole game...5 HOURS! That's from skiping all the cut scenes. Is MGS4 a movie..no, but it's pretty damn close, and the series keeps getting filled with more cutscenes than gameplay.

Lastly i feel that long cutscenes are great, but throughout an entire game, it becomes a cheap way to tell a story. Many games have found innovative ways throughout gameplay (scripted events come to mind in CoD games), yet Kojima (and a lot of Japanese develops now a days) just throw cutscenes at you...it's like there's saying, "Here watch it...it'll explain everything, now you may run to the next cutscene...there you'll watch why you ran there" Splinter Cell has always been about raw gameplay, expanding on every feature from the last game, and that alone makes it the better franchise in my opinion.

Splinter Cell has been a good series in its own right, but this is no contest. MGS is legendary.

I will be getting Convition right away, but doubt it can beat MGS4. :D

MGS because Splinter Cell it's more piloted experience you always know how to progress; you just have to follow the path using the right equipment an movements at the right moment....while in MGS you also have also to study the path to follow in order to not get caught....MGS has also better AIs. It's story and contest is less realistic while the action it's more. Of course both games must be played on an high-level difficulty otherwise they are meaningless.

Metal Gear Solid... the game's story has depth

I understand it's your opinion, but for me, and many other long-time Metal Gear fans, it's the story depth and the presentation of the whole single player that stands out. Kojima is better at it than any other Japanese dev I know of.

Kojima's presentation is wonderful. The story itself, though? Not so much. It's convoluted, repetitive (HORRIBLY repetitive), and non-sensical a lot of the time.

Convoluted plot does not equal deep story. It just means it's convoluted. I'd call it directorial masturbation more than anything else. That doesn't mean you shouldn't like it but let's call a spade a spade here.

Repetitive? All Metal Gear games are connected to one storyline, dude. And it may be overly complex, but I still understand what they're talking about most of the time. And should I not understand a specific thing, I just look it up on the net.

But to each their own, really. I still stand by my opinion that it has one of the best storylines in a game ever.