Unpopular opinion: I really like Last Cave. Just had some pretty good memories there, and otherwise its just very peaceful!
I also am pretty fond of Fluorite, since I usually go there to sit in the corner and just watch everything happen, which is peaceful to me. Not to mention, I met some of my good friends in that map, so there's also a lot of memories there.
Really, all of the maps have had some sort of impact on me, or I remember a lot of things happening in them--South Pole and Bonfire are especially great at making me feel nostalgic.