Don't get a Hesse, either. Hesse made the crappy receivers for Century, and their overall quality control SUCKS. My three top choices (not in any order) would be:
DSA's factory gun or the STG58 rebuild they do on their receiver.
Arizona Response Systems
Azexarms
Which you choose depends on what you want. DSA makes a great receiver and a great gun, but I don't care for the muzzle brakes they put on their guns. Azex makes great guns with STG parts kits on Imbel receivers, but from what I've seen makes mostly 21" guns. ARS makes everything from 21" heavy barrel guns to 16" carbines, including a nice, handy 18" carbine. They also seem to have a better selection of post-ban legal muzzle attachments, too. I just don't care for the flamethrower effect and the huge noise of the DSA brake on a short-barreled gun, which is the length I prefer.
Azex might be willing to make you a gun in any configuration you want, you'd have to call and check with them. DSA is pretty swamped just making their factory offerings, so they're not real keen on custom work.
I don't think you'll go wrong with any of the above choices, just do some looking around.