Well the whole thing isn't in any given key. Having Am and Gm would suggest that the key signature would be that of F major, except that theres a B in the Em chord, where in F major the B should be flatted. The A#m throws everything off. Instead of trying to solo over it with any one scale, treat each chord seperately, if you base your solo around the arpeggios of each chord, using scale notes as passing tones, it'll be fine. What i'm curious about it does that chord progression sound any good? Seems unlikely.