My personal favorites...
Sangin- absolutely phenomenal layout for insurgencies. Varied terrain, outstanding city layout, brilliant prebuilt FOBs, poppy fields, etc. not too big, not too small. My all time favorite Afghan themed map.
Isla Duala- one of the very few legit African maps. It's easy to get burned out on constantly fighting Middle East terrorists. Using this map in conjunction with Massi's African Conflict unit pack provides a slew of wonderful African themed campaigns. So much variety and unique thought in this map as well.
N'Ziwasogo- see my earlier comments about Isla Duala. Another very unique map that can be used for any Jungle environment. And...the best ambient sounds on any map available. It's also Huuuuuuge.
Sahrani SMD- this map doesn't get enough pub. Huge graphical improvements over the A2 ported Sahrani. Great terrain variations and Alive works wonderfully on it as well.
Those are my Top 4. If not for the AI path finding issues on Clafghan, it would be up there as well.