My personal experience is as follows:
BM 14.5" fluted HBAR with perm. attached Phantom FS
RRA 16" M4gery with slim profile under HG.
I specifically held them both to see which was lighter, and they're about the same, just different... :)
What I mean is, the M4 was front heavy, but light weight overall, while the fluted HBAR is evenly weighted along the barrel, and the same weight, or maybe even a tad lighter.
Of course, it's not exactly apples to apples, since my fluted HBAR is 1.5" shorter than the 16" M4 I was comparing it to...
If I were doing it again (which I am) I would still go with the fluted, or even better, turned and fluted by Kurt's Kustom Firearms for the lightest possible barrel without an A2 profile.
Just my $.02 based on my personal hands on observations at the range, YMMV, etc.