Personally, Uplink in Blsck Ops 2.
Summit was the first map I ever played on in Black Ops 1 and to see it remade based on my favorite mission from Black Ops 2, Celerium, is simply incredible.
Another favorite of mine is Outlaw from Black Ops 3 because I love the old west setting, but I didn't care much for Black Ops 3s multiplayer and didn't buy the dlcs.