5. Scarlet Monastery It isn't too hard, it has a bunch of different wings and it has some fairly decent loot for the level. I had a hard time deciding between SM or Deadmines for my #5 spot, as I really like the big battleship in the cave thing. But in the end, SM has a little more going for it, even if it is a little played out.
4. Live Stratholme I find this instance annoying for the most part, however, I enjoy a little bit of theater in my instance runs, and when Balnazzar is revealed at the end, well...that is pretty awesome.
3. Blackwing Lair When I first entered BWL, I hated it. The Razorgore fight was too hard for my noob self, and then Vael just destroyed my guild for over a week. But then we beat Vael, got through the hectic suppression room, and took down challenging boss after challenging boss. It was a far cry from the straight on Molten Core fights, and I enjoyed the challenge an awful lot.
2. Upper Blackrock Spire I like this instance for two reasons. First, even with the 10 person cap, it seems to go by fairly quickly. Second, the boss fights, while not fabulous, are a nice preview of the skills you will need to progress in the Molten Core. Dealing with adds, fear and controlling aggro all come into play. Yes, the Father Flame event is not the best, but at least it keeps you on your toes.
1. Zul'Gurub Kind of an odd choice, but I just really like the instance. There is a nice progression in difficulty, as a newbie guild can down the Snake and Bat bosses, but it takes some skill to defeat Hakkar or Jin'Do. The loot is pretty good, and it is a very nice step up from UBRS gear. Finally, the instance itself is very well designed from a layout standpoint, more so since they reduced some of the trash mobs.
Sorry, I got a little wordy, but that is my top five. What's yours?