My J&T upper is the most reliable upper I have ever owned; better in that regard than any of my Bushmasters.
I'd say the quality of the Bushmaster components is a tiny bit better, but certainly not $200 better. J&T kits even have Colt fire control parts. J&T seems like they are a little better than Bushmaster at actually putting the upper together, just judging from the number of gripes.
The Bushmaster will have a mil-spec mag phosphate finish on the barrle. J&T's finish is jet black and matches the upper great.
The fire control parts are of equal quality.
The other lower parts of the Bushmaster are finished a little better (blacker), and the springs seem to be of a slightly better quality.
I doubt there will be any difference in accuracy between the kits. The Bushmaster shoudl theoretically be more reliable, but like I said my J&T kit was 100% reliable.
While the chrome lined barrel will last longer, the non chrome lined barrel will still last a very, very long time. More than most guys will shoot in a couple lifetimes. If you do wear your barrel out, they are easy to replace.
Get the flat top!