GI rod on all my 5" guns. It's easier to take apart, there's no real benefit of a FLGR unless it's a Sprinco, Hart's Recoil Reducer or tungsten rod, etc.
A one piece guide rod won't make a gun shoot any more accurate, a two piece guide rod can come apart on you and fly down range when firing. A regular stainless rod doesn't offer enough weight to reduce muzzle flip. IMHO it's a wasted expense to add one, and a feature that does nothing but offer an excuse for infalted prices on some models.