We are shotgun only here and I use both slugs and buckshot depending on how/where I'm hunting. Since buckshot does not travel as far as slugs I use it when the ground is frozen.
For buckshot you will have to pattern your gun, various chokes and different type/sizes of shells/shot, keep records of the pattern sizes and pellet counts. I've done alot of work on,and testing with my Benelli, it produces a great group out to 60 yards. What folks sometimes fail to realize is that buckshot looses alot of velocity after 50-60 yards and while you may be able to put pellets where it counts, they might not have the energy to penetrate far enough to do the job. With a good patterning gun and used within it's effective range, I don't know anything that puts deer on the ground faster than buckshot.
Slugs, you want a Foster style, Federal, Remington Sluggers and also try the Breneke, what ever produces the best groups from your gun, use the Cylinder or IC choketube. You can get rifle sights that clamp on to your vent rib.
This is probably my favorite deer pic, not because of the deer but for the hunt-(I used my Benelli this day). I tracked this deer in the snow all day, finally caught up to him standing where you see him. If you look up behind me you can see a small opening in the briars going back up the hill, it's about 50 yards to the top. I snuck up to the opening and peeked over the top, All I could see of him was his head and upper neck. There was 6 pellets in his head/neck, couple more through his ears and one knicked the spike, he tumbled foreward and didn't move(3.5" 12ga Federal-00). When I got down to him there was a very hungry coyote there wanting some free lunch, it's never going to be hungry again

...I think the deer saw the coyote and stopped which is why I got close enough to shoot.
Doug