Apples and Oranges.
It's hard to choose one fighting game over and it's even harder when the fighting games mentioned are both excellent and there's nothing blatantly wrong with them, i.e. inifinites, game breaking glitches, etc...
One is a very good 2D fighter that has garnered praise for it's smooth graphics, quick gameplay, and has an an expansion on the way.
One is a very good 3D fighter that has been touted as 'the most balanced of the entire series' with only ~3 of the cast not being 'tournament viable' out of 40 or so fighters.
So really it's all up to personal opinion and mine is: I like Tekken more.