I own both and put in countless hours with each one, and I honestly think Titanfall is the clear winner, the gameplay is near flawless and the progression system is top tier. Plenty of viable weapons, titans and loadouts to ensure variety. The dev support is great, the only thing holding it back right now is they need to release a couple new maps. The new live fire mode is sweaty as fuck but heaps fun, not to mention it is (like all the dlc) free!

Battlefield 1 is a beautiful game, and excellent map design, but that's about as far as it goes for me. Honestly it's the player base that has been the biggest negative for me and why I stopped playing it much, too many scouts or KD fiends not interested in ptfo. That coupled with DICE making poor decisions regarding weapon balance (not to mention a severely lacking amount of and somewhat boring weapons) and the rest of the bugs with the game it can just be a chore to play sometimes. I guess I've been spoiled by the many polished shooters recently (eg. OW, TF2) I feel the game doesn't feel complete yet and it won't for a while. But give it 12 months and it'll be as good as BF4 probably.

The best thing about both these games is you can expect them to be supported for a while, however keep in mind one is behind a paywall.