Marshes. It seems to me it's got the least amount of dickery of all the maps. Lots of cover mixed with a few open spaces, no ASF, great for all weight classes. Lights and Harassers can get away with hit and run tactics, while brawlers can mix it up in the various building groups or in the hills. Long range mechs have their choice of positions as well, and the hangars provide perfect APC parking spaces for BA spawn. Colour pallette makes it hard to see at distances, and that Fortress dropshp is kind of cool. I forsee a TC map based on Marshes, with a functional Fortress with weapon pods enabled.
Thunder Rift: Gauss, gauss everywhere. Also PPCs and large lasers. And that damned water. And those bridges.
Mirage: Eh. Nobody seems to take advantage of the mountainous areas off to the side, turning it into a gauss fest in the center.
Sandblasted: The rolling dunes on the left and right sides simply mean that all you have to do is sit back in a mech with highly placed weapons (Shadowcat or similar) and snipe at long distances. The center is pretty much suicide if the battlefront is there, since you'll be eating Arrow IVs and PPCs in short time. On the other hand, this map does seem to promote combined arms with regards to mechs, ASF, AA, and tanks.
Frostbite: Haven't played enough.
Clear Cut: Lag. Lag everywhere. Also, sniper fest, and ASF.
Inferno: I have to say I hated this map ever since yesterday. Falling through the damn floor, can't walk out the walls of the hangar, getting stuck on rocks or in lava pools with no exits.
Extremity: Incredibly better since the redesign. It's probably my second favourite map, although HDR really kills my eyesight during daytime. Low gravity makes playing BA easy and hard at the same time, while mechs have their advantages/disadvantages with regards to heat management. ASF don't seem as common, but I don't get much time on Extremity.