Mine are:
CS:GO
L4D2
Titanfall
and I've just bought BF4 on PC (again, after buying a couple of weeks ago and getting annoyed with it and returning it )
On Steam and Origin my ID/Username is MrRockliffe, so feel free to add me. I'm often online, but I've just bought a new motherboard, CPU and Case so won't be gaming for a bit.
I do have an XboxOne, so give me a shout on that too if you fancy a game. I have BF4 and GTA V on that, more to add soon hopefully. Gamertag is Sheep Sardine (no it's not because I live in Wales - didn't know what to use so I went on an online gamertag generator and that's what it came up with...)
So, what MP games have you spent the most time on?