Liberation: if you're a sniping champ, this map is for you. As mentioned, there's very little cover around from air support, Domination isn't very interesting as caps are very hard with sniper around every corner - you just can't cover them all so it becomes a game of chance that you're looking the right way when the defending sniper pops his head out. Would I buy this Solo? No.
Piazza: fast paced, narrow alleys and doors, tight corners. Definitely SMG and shotgun terrain. Of the three DLC maps, I've played this one the least (though, I wish that was liberation...) and liked it the couple of times I've played. Would I buy this Solo? Yes.
Overwatch: Love it! Mixed classes - all can do well if you stick to 'your' section of the map. The center tends to host some intense firefights with both levels having line of sight to each other battling over the center flag. Fighting for control of the B flag in Dom (you guessed it, dead center of the map) reminds me of fighting for B flag on Lockdown. Bring friends to make a successful cap - and have some of them sweep the top floor before you go in for the cap! Would I buy this Solo? Definitely.