Capture & Hold is fun but it's too chaotic for me. I just end using Brute and spamming grenades, dying, then doing it again.
Found out that the custom servers allow full XP/Badge gain. The amount of XP you gain is more tied to time in a match rather than performance...which means that the 24/7 shrike servers (that are timed to end after 20mins) are the best way to rack up XP.
This isn't me, but it's from doing what I just described:
Without boost that's still like 5000+.