The BF3 campaign was definitely fun, but the story was confusing and terrible.
However, everyone knew what was already gonna happen in MW3, (Makarov dies big woop)
BF3 was new and refreshing, but it needed a better "story". It was very recycled and very anti-climatic at the end.
The characters are also very blunt, except for Montes who is the only person that truly shows emotion.
If you have the choice, BF3 because its fresh. It's not the best, but its new.