+1 Best maps in the game right now are Vertigo and Mirage, for two different reasons.
Vertigo is the most dynamic, interesting and fun map to play and watch. Mirage is the most balanced and competetively viable map in the pool.
Cache, Cobble, Tuscan (yuck) and Aztec have nothing to bring to the table in terms of a real competetive pool.
Cache has been tried over and over again but it's just a one-dimensional aim map with not much going on. Imagine arT playing on Cache - what the fuck would he even do? The map is so stale and outplayed and allows for so little creativity that the most interesting play that's possible is a site fake, and even that isn't very convincing considering how closed off the skybox is. Fun to play MM, trash for competetive CS.
Cobble has been changed oh so many times now that it's unrecognizable and it belongs in Casual at this point. Perhaps with a full overhaul it could be somewhat viable, but they would have to ruin the original Cobblestone layout even more to do it. So is it really worth it?
Tuscan is similar - it was made for a much, much older version of CS, which worked very differently from GO. The timings are off, and the game mechanics don't suit the map anymore. I really hope this never becomes official, especially not replacing one of the 7 competetive maps we currently have, all of which have been tweaked over time to account for the changes in our current version of the game. If you want to play Tuscan - play 1.6.
Aztec I guess is an option for the future, in a way similar to Vertigo. Vertigo was completely different in it's old state, and when it was updated really the only thing it had in common with the old map was the skyscraper theme. I think Aztec would be able to pull off a similar thing. The difference is that Vertigo replaced an obviously flawed map in the pool (Cache), the weakest link if you will, while Aztec is not a clear replacement for anything. Sure you might think Mirage needs a graphical overhaul, or that Dust 2 gets stale to watch so many times, but they are very viable competetively even if you yourself dislike them.
If we're looking at the professional 7-map-pool: Don't change a fucking thing. For once in the history of the game we have a map pool which is fairly balanced and interesting.
If we're talking about the game itself, like Matchmaking and the other gamemodes, I couldn't care less what they add. I'd love to play Aztec, Tuscan, Cobblestone on Matchmaking. Ruby was one of my favorite MM maps when that was in the game, such an interesting map. But I don't think it, nor any of the other maps I've mentioned, is competetively viable for professional play.