In order of preference:
- Broken Steel (You get to continue after where you normally would die, the level cap is increased to 30 and enables some good perks and I get to see Liberty Prime blow some more shit up)
- Operation: Anchorage (Only because it nets me the Chinese Stealth Armor and can get you unbreakable items if you use the Gary 23 glitch)
- Mothership Zeta (Plenty of neat weapons and ammo, plus some Alien Power Cells. I absolutely loved the bit where you get to...
...shoot down a hostile alien ship. That was epic.)
- The Pitt (decent overall, got confusing at one point and has some great loot, but that's only if you can be arsed looking for all 100 steel ingots. Christ, that was a pain. Thank God there's a mod for the PC version that makes them glow bright blue so I didn't have to pull up a walkthrough for it again after my computer was formatted)
- Point Lookout (Ridiculously overpowered enemies, not much loot and it was pretty underwhelming to me. The highlight for me was the Mother Punga, that part was hilarious.)