I grew up playing the Hitman games ALOT, as I never really played that much of Splinter Cell.
Splinter Cell in my opinion is a really good game and I have gotten really into the trilogy as I am alot older now and can actually beat the game without getting stuck on ammunition on the first mission
But I am going to have to be biased towards Hitman Absolution as it's a Hitman game hasn't been seen since 2007 (Blood Money), apart from the trilogy ofcourse but that doesn't count and the fact that I have spent way over 200 hours playing Hitman: Blood Money when I was a kid.
I platinumed Hitman: Absolution and just bought the Splinter Cell trilogy a couple of days ago. I remember playing the first Splinter Cell on my friend's Xbox, when both the console and game were brand new. I remember it being very well done for it's time.
The only things I can say based on my amount of exposure is:
1. Hitman: Absolution is a very good game. Like, really, very good. Lots of replay value and;
2. The Splinter Cell trilogy looks to be 3 of the hardest platinums ever (like, 8/10 and higher).