What used to be the case for swamp rat was that they did a lot of the SR101 where most of Busse was Infi. I think after the battle grade Busse's became more prevalent, you saw a lot less swamp rats come out. SYKCO is still probably best defined by having the resiprene handle.
These are very rough guidelines as there is a bit of crossover over between them all, though SYKCO (most budget) rarely delves into the Busse territory with the exception of Busse basic's with resiprene and then SYKCO with infi, which is even more rare than swamp rat having infi I think.
Busse, of course, tends to have the most machining features like CBT, fullers, etc. I really like the swamp rat line as I'm a budget kind of kind, but mostly I really like SR101.
This is your standard swamp rat "grade" with the middle being the infi ratweiler that blurs the lines into the Busse features category. All are ratweilers.
Battle Grade Busse which blends into the swamp rat "grade" with good designs and SR101
Typical Busse "grade" with CBT, swedged slip, highly sculpted handles and infi.
I think this is a good comparison of what you pay for in the Difference in Busse vs Swamp rat. Very similar knives, ratweiler and nano fusion forsaken steel heart. Keep in mind, the infi ratweiler adds a fuller so it's slightly more feature heavy. You can see the CBT, more sculpted ridges on the steel heat, and a little more intricate design, often some fancy stuff at the pommel as well.
Typical SYKCO "grade"
Blurring of SYKCO and Busse "grade", which rare
Hopefully this helps with the distinction between the brands, or "grades" as I like to call them as it helps distinguish the basic character/feature level I'm looking at when looking into the Busse or Busse kin knives. It's not quite what you asked for but if you're new then you may be asking this too, as I had a hard time figuring this out a couple years ago when I discovered Swamp Rat through a great trade (the ratweiler) and then into the rest of the Busse madness (protect your wallet).
SYKCO is hands down a great value for some sharp you just want to beat the shit out of. Swamp rat gets into premium knife category and Busse is top tier, easily competing with custom knife levels with the exception of guys that craft freaking historic grade stuff that run thousands of dollars, though I think a few Busse's from the custom shop fall into that category as well (look at the recent ganza post and you'll see some high-level awesomeness).