Battlefield 1942, only singleplayer, same with Forgotten Hope.
Battlefield Vietnam, only singleplayer
Battlefield 2 was when I really got into the series and multiplayer. I can't remember how much I played, it's in hundreds of hours. Once FH2 was released, I stopped playing vanilla BF2 and I now have way more hours in FH2 than in vanilla.
Battlefield 2142. Bought it pretty late with only a couple of servers running at the time. Most were playing the Girbraltar map non-stop, with infantry only and no friendly fire. Just constant grenade spamming and just pure rubbish. Stopped playing it quite quickly, I played the demo more than the actual game. Most of the time it just felt like Battlefield 2 with new skins.
Battlefield 3. Played 50 hours and stopped. The series went too close to CoD with quick-grenading, quick-knifing, narrow and small maps and too fast paced game play.
Haven't bothered to even try BF4.