Grind is the best map for playing demo/dom. People spawn in your face and its easy to get streaks.
Mirage is ok except the indoors, I hate them
And Downhill is also ok, I like the whole map overall.
Hydro is bullshit, I simply hate it. All gunfights are just in the centre of the map and it's a gunfight of 4v4, 5v5 or even 6v6 (atleast when I play). So if a member of your team dies in that gunfight you are fucked...