I have traditionally used Bushmaster (built over 100 of them from ~2003-2006), but they're getting a little difficult to justify and a lot difficult to find these days, so I have reverted to using their SOURCE provider, Cerro Forge. Spikes, Aero, DPMS, Bushy, Daniel Defense, Anderson Arms, and many others use Cerro Forge receivers, so it's very easy to find them, and I have never had an issue with fitment or quality with Cerro Forge receivers.
So that's something important to keep in mind - 2 different forged receivers might have different names stamped on the left side, but that doesn't mean that they're actually different products.
Billet receivers tend to run a little thicker/heavier also, due to the alloys used and the manufacturing processes. Billets are NOT as consistently identical around the industry either.
So the long and short of it - I use Cerro Forge receivers as often as I can. I have a couple Brass Aluminum receivers (Square forge mark) that I'm very happy with as well, so they're my back up forge if I can't find Cerros, or if I find a great deal on them.