Bull, or heavy, barrels are used for different reasons. First, a heavy barrel tends to dampen barrel vibrations which, theoretically means more accuracy. Second, a heavy barrel does not heat up as fast as a skinny one and, again, theoretically will last longer since heat is really what destroys a barrel. Finally, a heavy barrel, within reason, makes for easier holding on the target since it will absorb some of the shooter's shakiness when his heart is pounding like a trip-hammer.
Now, having said all that, is a heavy or bull barrel better than a skinny one? Well some skinny barrels shoot just as good as, and sometimes better than the fat ones. Also, if you have to lug a rifle up a mountain slope or across that mile-wide meadow to get a shot, then you'll be thankful for the less weight.
So, there's no easy answer to you question. Ain't that the way it always is?
I'm sure you'll get a lot of input from other shooters.
I'll second Cheechako's comments. Bull barrels do make shot repeatability easier by absorbing the heat, vibrations, etc, better. If you're target shooting where you know you'll shoot a lot of rounds in reasonably close succession then a bull barrel is probably the better option. If you're using a hunting rifle with a skinny barrel that shoots well, I'd leave it alone! When hunting, you're only going to shoot a few rounds at best and probably occasionally as well. Heating isn't a problem then and you also enjoy the rifle's carrying qualities. No bull!!