I think to say one is better than the other would be a bit of a logical fallacy. They all have their merits and lack thereof in different departments. I love COD, whether its the classics or, contrary to popular opinion, the newer, futuristic titles. They all look really good and they're great fun in multiplayer and singleplayer. There's always a good amount of fresh content with every release and the maps are awesome. Nuketown is probably going to go down as a classic in gaming history for a long time. Same applies to awesome maps like Rust.
But Battlefield, for my own reasons, holds a special place in my heart. I much prefer the more realistic approach, the vehicles, the massive maps and of course the awesome weapons and settings. Battlefield 3 and 4 were modern warfare at its finest and Battlefield 1 brought it back to this awesome and wild WWI setting with its unique guns and crazy maps. And horses!