It really depends on what you like or want to play.
Uncharted gives you a mostly brainless linear shooter fest with good cinematic values and story. These are good if you don't want to put in a huge investment of time.
Witcher 3 will give you a more engrossing game that will require a huge investment of your time and will be mostly spent doing little quests multiple times with also an interesting main questline.
They are completely opposite types of experience. Aside from that all i could offer would be personal opinion. I'm an RPG fan, so i would go for the witcher. But, i enjoyed Uncharted 3 quite a bit aswell and 2 was alright. Uncharted 1 wasn't as satisfying though.







