What you're talking about here are two different games, almost entirely. They live in the same genre, and have similar concepts, but that's about as far as it goes. Splinter Cell is much more realistic, the tension is a lot thicker and the plot is much darker. Sam carries two guns, and only a handful of gadgets. Snake packs a small armoury in his pockets, and carries enough items to start up his own convenience store. Sam takes on terrorist warlords, Snake takes on 50 foot walking battle tanks.
To put it simply, if a stealth game is what you're after, stalking from the shadows and picking your fights, then Splinter Cell is what you need. If you like a little more action in your mix, and love a detailed story, then Metal Gear Solid is the way to go. They cater for seperate audiences, best to decide which you're a part of.
Or like me, just play both. They're equally awesome.
