Busse is run by Jerry Busse. It uses INFI steel (proprietary to Busse, and some times Scrapyard gets their mits on extra steel). INFI is super tough, even at higher hardness. It does not rust or stain easily when stripped or satin finished. It can bend, and take huge stress and impact without breaking or taking a set, or blowing out the edge. It gives up a bit of edge retention in the area of slicing (IE cutting cardboard, or slicing rope etc) from some of the other "super steels" out there. It more than makes up for that if you are doing impact work like chopping. Very easy to maintain a sharp edge. No special tools or diamond stones needed to sharpen.
They are working on a higher harness higher wear resistance version of Infi. I had a BAD which was treated a few RC points higher that seemed to hold a bit better edge in a small, thin, slicer. The new version (yet to be released) is supposed to be even better in that application.
Swamprat is run by Jennifer Busse (Jerry's wife). It uses primarily SR101 steel (modified 52100 steel, a great ball bearing tool steel). They also use a few others occasionally. Every bit as good looking as Busse. Sr101's primary weakness (if you want to call it that) is corrosion. It is a tool steel, that is prone to rust, if not cared for. If coated, you don't really need to worry about it. If stripped, or satin, you need to be aware, and keep it protected, or just let it patina if you are cool like me (I don't mind carbon steel, all stained, and grey !)
I think, in the smaller knives, Sr101 shines above INFI! I think it gives a bit better edge retention for the performance and toughness. Infi is super tough, but in smaller knives, you don't really need as much outright stupid toughness. I am willing to trade some "tough" for some more edge retention, and the ability to really go with a thinner edge.
Scrapyard is run by Dan, Jerry's brother in law (if I remember correctly).
Scrapyard originally used left over steel from Busse, designed to be tough, and have a huge price/performance ratio. They use Sr77 (a modified jack hammer bit steel), INFI (when they can steal it). Elamax recently, and a few other odds and ends like D2 and CPM 154 (if memory serves me correct?). Can't be beat for the price! Super tough, though geared toward utility, and not beauty!
They are all made at the same shop. Same stellar warranty, and the same great people working on getting them to us!
I recommend all three! Though, I have to be honest, I only have INFI in my stable right now!