Just judging past Splinter Cell and Metal Gear games, the Splinter Cell games are definitely more complex with the light and sound meters. One of the problems with the older games was the AI getting wonky because of all the ways they could detect you. Like, you would be sneaking up on an enemy and without any indication that they've heard you, they go right into the combat mode and shoot you. Gets really annoying when all your planning is ruined by some janky AI, but when you do pull it off, it's great. Other than the AI, the splinter cell games were very stiff with how they control, especially with all the context sensitive stuff (Conviction looks a lot more smooth).
I really like Splinter Cell games and MGS games, but I do like MGS games a bit more because everything feels more fluid and more arcade like.
Also, Hitman games are great stealth games too. I'd even say that Blood Money has more variety than either Splinter Cell or MGS. I want another Hitman game.