I guess we have the "one is an apple, the other is an orange" scenario here..
CoD: AW is it's own game, with Titanfall flavours, but at the end of the day it plays like a CoD and is a CoD game.
Titanfall is Titanfall... Simple as that.
Both are great games, personally if you're looking for more of an active game and knowing you're paying for a decent game that has a vibrant community still active in it. Advanced Warfare might be for you.
Titanfall is a great game in it's self, but honestly, the game is pretty dead. Alot of people play it, but not enough to able to say "yeah... people play it".
If I were you, I'd watch some gameplays of both games, see which one appeals to you more, and go from there.
At the end of the day...