Do yourself a favor, don't shoot rifled slugs in your rifled barrel. They might actually shoot ok, but you will get lead in your rifling and it will be a pain to get out. Stick with sabots.

There are no universal truths. You really need to try some brands of sabots to find the ones your gun likes best. I use plain old 2 3/4" BRIs and they shoot great. Just about any 12 ga slug will wilt a deer real quick. Focus on accuracy. When you think about it, you'll probably spend more on gas than ammo, so in perspective, it's worth it to buy whatever works for your gun.