Most of my factory barrels are accurate, not benchrest quality, but more than accurate for hunting. The 223 barrel I have is a tack driver. 5 shots in less than an inch all day long. I got that barrel used for less than a third the price of a custom barrel.
Deer & bear, 7mm and up will work fine. The 284 is a lot of case capacity for a 15" barrel, the 7mm-08 might a more efficent choice.
Not sure I have a favorite barrel, but I did have a loaner from OTT in 445 super mag and it was a hoot to shoot. A rechambered factory 44 with the OTT shark gill break. I was getting 2,000 fps with 240gr pills. Here's an unlucky charlie that fell to the 445.