I have had one 20" Green Mountain Fluted an have built 3 other 10/22's with 20" Green Mountain 20" Fluted Barrels. All have shot quite well, at least to the owners expectations. I also have built a couple with 20" KIDD Barrels. For me personally I would have to say the KIDD Barrels have shot slightly better. However the difference between what brand & type of ammo a particular barrel likes will be a lot more difference than the difference between a Green Mountain and a KIDD, all other things equal.
Also had an old Butler Creek 20" Bull Barrel that shot quite well also.
Larry