Well, I rather like my BAR in .300 Win Mag. My latest favourite, tho is my Beretta Storm CX-4 in .45 ACP. Shoot, I'm still right fond of my Winchester .30-30 that inherited from my grandfather.
The wife put her 2 cents in - she votes for the PS-90. I got that thing last year from a buddy while he was going to be out of state for a year or more for work...I never get to fire it since she always has her hands on it!!!
It has to be either my Spikes Tactical Ar15 dedicated 22lr or my 10/22. Both are cheap to shoot. Both are very modular. Both have a world of support in the aftermarket.
AR-15, there is just so much you can do with these rifles. All kinds of "goodies" to hang on them, and if you don't like 5.56mm, there are several other calibers and barrel lenghts just by switching uppers.
I have to say my Calico M-100! It really draws a lot of attention. I can load up 10 100rd drums and shoot all day without reloading! There's something so fun about your finger getting tired before its time to reload! Plus you don't feel guilty shooting that much cheap 22!