I wanted a plain Jane style FF Tube (no rails, just smooth) on my Varmint AR. I ended up getting a great deal on an RRA, which is very nice quality, however it has some heavy knurling on the grip area, which I don't prefer. The deal was good, so I can live with it. I'm happy with the tube, it's just a little more "grabby" than I was looking for.
My brother built a Varmint AR and got a good deal on a DPMS upper, with FF tube installed. I like the DPMS tube better than my RRA tube. It is solid, and very well built. We had some issues with the how the upper was assembled (we bought it NEW from DPMS in person at a gunshow!). So I dissassembled the upper, and fixed the problems.
The DPMS tube is a very nice, quality built tube (I think we just got an upper that was put together on a bad gunsmith day, but all problems are fixed now).