In no particular order:
Caesar for being a true visionary.
Raul for being an allround cool dude. Love the Mexican theme, wish NV had more of it.
Hanlon for being the only character I felt sorry for in the entire Mojave. (I usuallu play Legion, but it always pains me to do his quest)
Julie Farkas despite her naive idealism, cant help bit wish she had more quests.
Follows-Chalk, the only companion besides Raul which I found pleasant to follow me around. Too bad I couldn't take him to the Mojave.