DSA make the best in my opinion, since they got the blueprints from Steyr and FN and are forged, differencially heat treated and really well made.
Coonan used to make some nice cast ones for Federal Arms but when Fed Arms went Tango Uniform they kept the rights to the receiver/machinery and so Coonan is now having to redo all the work. Hopefully they'll have some out this year.
Imbel, very hard to get right now, made to FN spec in Brazil. Some of the later ones might need a little more tweaking to get to fit right.
My experiences with Enterprise have been entirely negative. The L1A1 receiver they sent me a while ago made some of the crap that the angry gun monkeys at Century make look good.
That's about it.