Skyrim for me was a better experience due to the fact it's more open. I'd end up drifting in to some unknown town and doing side quests totally forgetting about the main storyline, plus there's the endless amounts of modding options. Witcher 2 looks phenomenal and is the kind of game you'd play through once or twice then you've done everything.
Witcher 2, no contest.
Thanks guys i got skyrim , whats the best mods to get for it? want to play it with all bells and whistle to start with