Jal5,
I hunted with a Mossbergg 500 for many years, using the regular barrel, modified choke tube, and Federal foster-style slugs, with very good accuracy. The Federals (1 1/4 oz) worked the best for my gun, but slug guns will vary.
I now use another 500, with a cantilever scope, rifled barrel, and I've found the Remington Copper Solid sabots to be the most accurate, although close seconds were the Federal/Barnes sabots, and Lightfields.
I had the cylinder-bore barrel, but never used it.
Hope this helps.
MH