I would say CGI, most definitely.
I just think that a live-action film could go wrong too easily. It would probably be incredibly difficult to find actors that portray the characters accurately, and it would probably result in the film feeling too distant from the games.
Whereas, with an animated film, the makers can make the characters look however they want, they can hire the same voice cast as they had for 'Curse' (which had the best voicework out of all of the games), and they could also create a cool artistic style that they wouldn't be able to achieved with a live action adaptation.
Read that instead ^.