In my opinion the best CQC airsoft guns are GBB pistols. For CQC I'd opt for a sig over a colt, simply because its shorter and I don't like the look of a colt any shorter than the M4. You should also consider other guns like an MP5, P90 or G36C.
You won't realise how much of a difference gun size makes in close quarters until you end up like me. I like woodlands so I got a full length G36. I played outdoor CQC once, and it was really difficult with my gun.
Guardians of Asgaard - KF32
VFC H&K 416C
VFC KAC SR16 JL Billet SBR
TM FN Five-seveN