What makes for the most accurate slug gun?

I've looked at the Tar-hunt slug guns, bolt action, 1:28" twist rate on their rifled barrels, but certainly not looking to spend anywhere near that kind of cash, $2500+

The savage slug gun looks pretty similar to the tar-hunt, but I think I read it has a 1:35" twist rate? For a 12ga...1:23" for a 20ga. What are the twist rates for other guns in 20ga, anyone know?

Do you think 20ga slugs are inherently more accurate than 12ga slugs? If I get a new slug gun I plan to get a 20ga.

Not a big fan of cantilever barrels/scope mounts, but if a more accurate slug gun has a canti I wouldn't oppose it necessarily either.

What about semi-autos vs. pump action vs. bolt action slug guns? I would assume a bolt or pump might be more accurate, is this right or don't you think? I've only shot semi autos and wanting accuracy thinking a pump like an 870 or bolt like the savage might be the way to go...

I've always thought 2 3/4" slugs were more accurate, but read somewhere that longer/faster the round the more accurate usually? is this true? Maybe 3" would shoot nicer in my current set ups. Either way I think I want an accurate 20ga slug.