Combat shotgun - I love it I don't know why but its an extremely satisfying weapon the look, damage output, everything about it
Hunting Rifle - I loved the hunting rifle especially in New Vegas when it was made more deadly and an affective weapon however I loved it in Fallout 3 but it just wasn't deadly enough but christ I loved it.
Fat Man - *Ding* enough said
If I got a bonus weapon it would be the Railway rifle [censored] that was fun.