For a fixed, always up BUIS I'd go with a LaRue or an LMT.

For a folding BUIS I'd go with the Troy or the new MI low profile. MagPul will be releasing a new one that they showed at SHOT this year, I'd like to try one of those.

I'd avoid the DPMS rear as I had one and had trouble with it.

The ARMS folders are okay if you remember to install them per the instructions and use loctite on them.