The revolvers I've shot haven't ha full underlugs (then again, I need to get and shoot more revolvers). I like the way both of them handle, and one's an RG. Yes, I like that RG. Its a .32 S&WL, which is a dying caliber that I like (thank God for .32 Mag and .327 Mag). However, the revolvers I've shot, without full underlugs, and the ones I've handled without, just feel better and more natural than the ones with full underlugs. The security (or something, could never tell them apart) six I handled felt better than the full lug GP, which just felt a little top-heavy.
I'd have to shoot both, though, to know for sure.
Also- the M28 felt better than the 686. LONG LIVE THE N-FRAME .357! THANK GOD FOR S&W BRINGING IT BACK!