Most of the paintguns I've owned either came with decent to great stock barrels or had fixed barrels. Notable good stock barrels were my original SL-68II (honed & polished, though), my F2 Illustrator, all of the Palmer guns, and my current Custom Pro. I also stayed stock with the Angel, Bushy 2K, and other random guns I owned, but those mostly came and went too soon for me to spend money on upgrades. I tried a BOA on the SL and an Armson on the F2, but neither improved the performance and the Armson was decidedly inferior.
My other two guns are both WGP-threaded. The Wrath LTD came with a 14" ported barrel that's ridiculously light and pretty open-bored. I think I've shot a few hoppers through it, but usually it stays sacked. My preferred barrel for the Wrath is a short Dye aluminum with a Lapco .682" sizer, and my preferred barrel for the Sniper is a 14" Custom Products 1-piece in .682". I don't even have the original barrel for the Sniper. I've got a 12" SP AA, too, but I really don't use it.