As Tally says, this gets beat to death.
#1 buck is more effective than #00 or others.
#1 buck is going to be more effective than a slug if you can keep the shot on target and are not shooting through a barricade.
Federal Flight Control buck has a wad system that keeps incredibly tight groups for very long distances.
Most slugs are soft and don't perform through barricades as well as you'd think. If you want penetration, look specifically for a hardened slug.
Me, my 870 is loaded with Federal Flight Control buck #1 (LE1321B) with a few Dixie Slugs IXL DGS hardened slugs in the side-saddle in case I need more penetration. There are other choices for hardened slugs as well.
I suggest folks read the various things Dr. Roberts has written on ammunition performance. He is an expert in this field and has been very good at explaining the real world performance issues as well as sharing the testing results of various ammunition. I included a link to his summary on shotgun ammunition in an above post. I would suggest you seek out his other writings as well. He posts a fair amount in the Terminal Ballistics Information sub-forum on m4carbine.net (username DocGKR). Don't neglect the stickies in that sub-forum. There is a lot of good info there.