Rightly or wrongly, there are people that think that chopper lump barrels are better. I guess its possible I'm slightly prejudiced on this issue since I bought a gun with them, but here's a desription and discussion of chopper lump barrels from Hallowell & Co:

Chopper-lump bbls (also called Demi-bloc barrels) - A method of joining the two separate tubes of a set of barrels where the right-hand half of the pair of lumps under the barrels are forged integrally with the right barrel and the left-hand half of the pair of lumps under the barrels are forged integrally with the left barrel. Chopper-lump barrels can be recognized by the fine joint-line running longitudinally down the center of each lump. This method of jointing barrels is the best because: 1. It is the strongest in relation to its weight, and 2. Because it allows the two barrels to be mounted closest to each other at the breech end, reducing problems regulating the points of aim of the two separate barrels.