All of my ARs are range or hunting rifles. When I built them I did not want to use, or have any use for a tactical quad rail type forend. So for my first build, I settled on a Armalite fiberglass tube. While heavy, the thing is bombproof and I have been very happy with it. Sadly, I do not think they have been made for several years. On my 6.5G hunting carbine, I initially went with a JP mid length tube. The concept, function and fit are first rate. I hunted with it for a few seasons, and decided to replace it for 2 reasons - aluminum tubes can make some noisey unnatural sounds when knocking around in the woods, and hanging on to an aluminum tube in frigid deer hunting weather does not enhance ones hunting experience. So I replaced the JP tube with an Alexander Arms G10 tube, and it has totally satisfied my needs.
For anyone else still hunting for options, the PRI carbon fiber tubes are great, but are pretty spendy.