You don't mention what you are hunting but I'd guess it's white tailed deer. Any 20 gauge slug will cleanly take any deer so I suggest that accuracy should trump ultimate power.
Slug guns are about the most finicky of cartridge loading firearms and the difference in accuracy between different slug loads can be pretty dramatic. MidwayUSA.com lists loads from Rotweil, Brenneke, Winchester, Lightfield etc. They range from 3/4 to 1 ounce and from 1476 FPS for the heaviest to 1800 FPS for the lightest. No deer can live on the difference.
The loads with skirts or wads that stay attached seem to have pretty good reputations for holding tight groups downrange.
I recommend that you grab a box each of several loads and see what groups best at the longest range you expect to hunt at. Then I'd shoot what my shotgun tells me it likes best.
Good luck and happy hunting.
Lance
