These are my top five:
1 - The Crumbling Isle - Love the isolation and the ruins, usually use the 64x64 lot
2 - Mua Pel'am - Again love the isolation and the waterfall, good place for off the grid play
3 - Spice Market - Love this district for vampires as there are always sims walking around
4 - Cavalier Cove - Has a nice country feel, very peaceful
5 - Forgotten Hollow - I love it's creepy dark feel, and I play with a lot of vampires
Honorable mention goes to Belomisia Jungle. The jungle is beautiful, and I've yet to get tired of exploring it.