I'll start,
Caustic Valley, north/northeast (B5,C5)
http://mwo.smurfy-ne...lley&m=skirmish
This sulphurous/volcanic spring area is just cool. It's mostly flat, but there are plateaus that subtly vary the elevation, and the sulphur rocks break up sightlines and provide cover. So if you manage to get an engagement with another mech inside this terrain without any interruptions from outside, it's really neat. But that's just the problem... the tall rim of the caldera has line of sight to just about every bit of this terrain, so you *will* get interrupted by mechs from the outside, and that makes this a place you don't want to fight in... which is unfortunate.

Sulphurous Rift, E7
http://mwo.smurfy-ne...ands&m=invasion
This area is pretty much identical to the area I described in Caustic Valley. And that's why I like it. This area has the benefit of not having a tall-*** caldera overseeing the whole region, but ... it's a dropzone, so you only fight there when there's dropships involved, and that's unfortunate because the bumpy terrain and tall sulphur rocks for cover make for a neat engagement area.
Grim Plexus, H5
http://mwo.smurfy-ne...muth&m=skirmish
I hate the majority of this map. But this region is largely flat-ish, with nice undulations, and the vertical pillars offer plenty of good cover. You can ridge-peek here, you can side-peek, you can brawl, you can do midrange, it all works. This area is ... unsurprisingly, really similar to the sulphurous areas I described above.
Terra Therma, the entire map
http://mwo.smurfy-ne...orld&m=skirmish
Okay, so what I don't like about this map is the layout - there's big chokepoints leading toward the middle from every direction, so you end up with entire teams fighting at chokepoints more often than not. But if you get to fight literally anywhere except for the middle of the map? It's fantastic and I love it. H7 is a really cool area, but so is D7 and E6. I really like the F4 region, but nobody goes there because it's out of the way. =[
Forest Colony, the forest part F7/G7
http://mwo.smurfy-ne...lony&m=skirmish
What I like about this area is there is a north-south-aligned ridge dividing it into two sides. And from both the east and west sides you can back up and trade across the ridge at a distance, or you can charge straight over and brawl. The ridge isn't really a ridge per se, but a consequence of the undulating terrain in the area. But what really makes this area great, is there are large trees scattered throughout, and they make great cover for side-peeking mechs, so really any kind of mech can fight in this area. I just wish it wasn't so small, I wish we had a map that comprised entirely of just this forest terrain. Oh, and the part I don't like about this area is there is a tall plateau, the northwest corner of H7. You know what I'm talking about. It overlooks the entire forest area, so fighting in the forest area isn't really that safe as a result. Just like what happened with Caustic Valley... a really fun area to fight is ruined by there being a powerful vantage point overlooking the entire region. Blegh.
River City, F8
http://mwo.smurfy-ne...city&m=skirmish
Holy crap if you get into a fight in these tight alleys between buildings, it's bloody exciting. I want more of this.
Polar Highlands, everywhere EXCEPT THE CENTER
http://mwo.smurfy-ne...ands&m=skirmish
The center of this map... like so many MWO maps... ruins the entire map. If the center of this map was the same terrain as the rest of the map, with all the Hoth-esque trenches, this map would be absolutely fantastic. And indeed, when you get a Conquest match on this map and people largely avoid the center because there's no capture points in the middle... it's great!