I will dual-carry when my clothes and occasion allow, but the one gun that is with me 100% of the time is my LCP. My most common dual-carry rig is a LCP in a Uncle Mike's pocket holster, and a M&P 40 in a Conceal Carry Concepts Looper (IWB) holster.
LCP - Remington Golden Saber 102gr
M&P 40 - Federal Premium HST 165gr
Either would be enough to give somebody a bad hair day.
I carry a Springfield V-12....45 acp. Night sights, Loaded up with Hydra-shocks. Wilson combat 8 round mags. Fobus holster for off duty. Safariland 6004 for on duty. I like the V-12 for the decreased muzzle flip for the second round of double tap. The sectional density of the .45 makes it a real good man stopper coupled with the Hydra-shock slug you are less likely to over penetrate your adversary. I carry a S&W .38 spl for back up. Cause you never know when MURPHY will show up.