If you do trade, just trade upper halves. That way you keep your own serial number. The lowers are equal quality, except his RRA probably has the 2-stage trigger which would be lighter than yours.
If you don't shoot ammo heavier than 69gr then you have nothing to gain from the 1/7 twist. If his is a true M4 profile it'll be about 1/2 lb lighter than your HBAR. If it's new enough to to be 1/7 twist then it probably is, but I think RRA used to make (maybe still does?) barrels with the M4 cut in front of the front sight for the look but still HBARs under the handguards, which would weigh just as much as yours. Bushmaster uses 4150 steel which is better than the 4140 RRA uses, but the difference is in how it handles high heat so you wouldn't notice unless you shot a lot of rapid fire. ("Normal" non-AR rifle barrels are 4140.) Bushmaster barrels are chrome-lined, which is easier to clean and lasts a lot longer. Not all RRAs are, but his might be. Personally, I want to be able to shoot the 75/77gr ammo and I'd want the lighter profile so I would take his barrel as long as it were chrome-lined. If his is not chrome-lined, then I'd probably keep the BM.
Another option would be to just trade upper receivers and keep your own barrel. The upper receivers are equal quality and if you get the detachable handle too you're probably coming out ahead. I see you're in Indiana. Drop over to the Hometown forum and I'm sure you can find somebody there who will help you do the barrel swap if you choose to go that way.