anyone know of any good manufacturers that make a nice 9mm upper?

ASA
COLT
OLYMPIC ARMS
ROCK RIVER ARMS
CAV ARMS

I hear bad things about ASA, and COLT is overpriced. I am getting RRA. I don't know anything about CAV ARMS. An OLYMPIC and a SOCOM magwell block use STEN mags, so that is the cheapest. RRA is a COLT knockoff. They use modified Uzi mags.

Help
Need 9mm upper 101

I have a 9mm uper on the way. What is needed to make it fuction properly? I know of the different companies that make them. Where I get confused is with the parts. If I understand correctly, some can be pinned on and are ready to go. Others need to have the hammer, buffer and other parts replaced. Which producers have which requirements? Mag applications for each would be helpfull as well. FYI  I have an all Colt upper on the way, but would like to hear/read about the other for  comparisons.
Thanks

Olympic is ready to go right away, Colt style need hammer, and a buffer. RRA is colt style, not sure about the others.

Oly uses a proprietary system, Colt, RRA, and ASA use modified Uzi mags, and I don't know about Cav arms. An aftermarket SOCOM block will make Oly use sten mags.