I go back and forth on which one I think is better, or which one I like more.
The first one holds a permanent place in my heart and will never budge. TWOW improved on so many things, and had a fantastic story filled world building. The score was weak though, and I missed the Na'vi language throughout. I loved that aspect of the first one.
There are also a number of moments in TWOW that I just really can't stand for some reason. I really hated the way General Ardmore's (Soprano's lady) character was introduced and portrayed. For a movie/franchise that's so hardcore about maintaining a world and environment that' plausible, she came off as such a caricature. Jim took the elements that made me eye roll at Quaritch's character in the first film and doubled down on them with her.
TWOW had a huge hole in it toward the end as well, when the Metkayina seemingly vanish from the final. I guess there was an enter sequence shot and rendered, but it was removed from the final cut. It made a 3:10:00 movie even longer, and test audiences said it broke up the flow of the film's final act. Apparently is was pretty brutal as well, from a violence standpoint. I hope it's included in a director's cut down the line, even though Jim has already said we aren't going to get one.
I think TWOW is the better movie. If I built out some sort of grading rubric and filled it out for both movies, I think it'd have a higher score.