Self cure resins are all in the similar category in my opinion. What makes one BETTER than the other is how the techs handle them and cure them.
While you can throw the two parts together on the bench and give it a few minutes it will get hard, however its dimensional accuracy and the amount of residual monomer will be drastically different than a properly mixed and cured by the IFU.
That being said your choice of material should be based upon what you are using it for and its intended purpose, If you are using it for quick same day repairs, add ons and transitional appliances just about any material will act the same.
If you are looking for something that is a bit more color stable and has less residual monomer in it for a more permanent solution, I would go with something like Ivoclars ProBase Cold, matches their Ivocap resin very closely and is very dimensionally accurate and works well in the fluid resin system/matrix style processing.
The GC line of NATURE-CRYL resin is another very versatile product that I use in my laboratory and love its properties. Can do fluid resin and repairs with good results.
Another good line is by Kulzer, The PALA line of coldcure works exceptionally well, and their PalaXpress ultra really is a bit different, they claim its the first coldcure high impact, It doesn't seem to be harder when you machine it but I can say that thin transitional partials post imd. extraction seem to hold up a bit better.
Like anything else PRICE is a variable and all of these resins will be a bigger investment over KEYSTONES, I prefer them and feel them make me more money in the long run with any of them.