The classic set of stoppers from BD is a must have for any rack. It includes the most used stopper sizes made by Black Diamond and for the price this package can't be beat. With great kN ratings, you'll feel way secure with these nuts of simple, yet effective design. And candy colors aren't too bad either.
This was the first I bought for starting the rack. Not much of a rack but with borrowed gear I still ended up using these alot. Nice shape, but need some narrower to have more options. As far as size, good selection, used the smaller ones most, but guess it depends on where you climb.
I'm building a rack to get out in JTree. These are a simple to place and reasonably priced. They aren't the lightest set of nuts, but probably won't be an issue since I'm not doing huge multipitch routes. I was able to set up a ton of fun JT toprope anchors with just this set, some long slings, webbing, and a #3 camelot. A lot of bang for my buck.
So as anyone knows, stoppers or nuts or whatever you want to call them are an essential piece of protection. The BD stoppers are perhaps some of the most popular out there. Most are comparable. These do have the extra advantage of having a loop of wire at both ends. The actual stopper can be slid down, looped over a feature, and cinched back up for another form of protection. One thing about this set is that it does have a size 1 or 2. Both these sizes are great for aiding but are only rated at 2kn each and are not rated to take real falls.