Although my underwear collection is huge, by far I wear 2xist the most.
My favourites are the Essential contour pouch brief. As others mentioned, men who need extra room should stay away from the no-show briefs.
I also have the trunks and a jock (purely a fashion jock and offers little support but does have ample room.)
As far as their individual collections go, I have:
Essential (best fit)
Varsity* (runs a little small and more room needed)
Retro (fine fit for your junk)
Campus* (great fit and material)
Liquid Cotton* (best fit for junk, but a little thin in the material)
Contrast (same as Essential, only with contrasting piping)
Pulse* (good fit; not too keen on the material)
Track (ok fit, but a bit small fitting)
Modal (good fit)
As far as I know, those lines marked (*) are not available in retail stores, but you can still find them online.