I am looking for a good preassembled 16" Dissapator Style Barrelled Upper, Who makes the best value?

Bushmaster make them, I have never seen anyone ele's advertise them. I have one and it is well made and shoots great.

Bushmaster.  IMHO, value should never compromise quality.

I have an Olympic Eliminator (dissipator style upper). Despite what some may say, I have now fired 1500 round through without a single malfunction. Depends whether you want chrome plated bore or not. The Oly has a match grade barrel. Don't know if the Bushy's is match grade but I know it is it is chrome plated. I get about 2 MOA with iron sights. as a bonus you get the muzzle brake included with the Oly.
I think Oly is about $100 less. I love mine, that's all I can say.

I think J&T have a dissipator style upper. Not sure of the price. there is another option for you

Model 1 makes one also.