Broken Steel was my favorite because it let you continue playing after the end game and the whole thing with the water caravans made the Capital Wasteland seem more lively and interactive, sorta...

Also the main quest missions were pretty epic at certain moments, I wont say any questline spoilers but jesus christ all of the explosions in that DLC.

On that note, i'll try and get up a post of my char headed to H&H after work, ill be brainstorming while im working. :rock