Polus and the skeld are both alright, but I like the aesthetic of Polus more. MiraHQ is too segmented imo, its too easy to keep track of where everyone is, too many long hallways and the massive cutoff between the reactor and the rest of the ship is a pain.
For now it's Skeld for me. Just because it's the only one that I 100% know by memory on how to navigate. I'm hoping at some point they let people make their own maps, that'd be dope.
I think skeld is just the best because I play it the most and its balanced compared to the other maps.