Halo is a wonderful series. Battlefield is also a wonderful series. However, if one must decide, I would have to go with Halo. Not only is there substantial lore and extensive plot involved with the Halo series, the Halo games themselves offer a little something for everyone. You can invest in a number of different difficultly levels throughout and extensive main campaigns, or you can work your way up the ranks via online Xbox live multiplayer. Needless to say, Battlefield is an awesome game, but it's just that... A game. Halo is a complete world with numerous opportunities for any gamer.
P.S. Not to mention the Halo books!
I wish i could vote both. I got bf1 this week. And let me just say this.It is great. But over this topic imma go with halo. Ive been with halo longer. Halo has a story, lore. Battlefield is a great game though dont get me wrong. Battlefield is realistic and is really fun. Halo to me gets kind of boring after playing an hour or so. Battlefield is endless for me. But i love both equally. P.S. COD SUCKS. It rips of halo.