My favorite companions for Fallout are:
1 - Willow
2 - Andrea, ARES Model 2.14
3 - Moria (FO3 merchant from Megaton. TTW version of the mod)
4 - Joanna
5 - Handy (Coito Ergo Sum)
If I didnt have any mods to work with, I'd have to choose Veronica and then Cass.