There are only about 3 or 4 actual epoxy manufacturers in the USA and all of the names mentioned above buy their bulk from one of those producers. Then they filter and add some additives for branding and mix ratio purposes. I can't find the abstract now, but RR and SS are from the same bulk supplier, I do believe. All of the surf specific epoxies contain a UV inhibitor. GR, RR and SS all do. The lower mix ratios are more tolerant of garage shapers mixing behaviors
2:1 or 1:1 can be 1.95:1 or .95:1 without much issue. The 5:1 or even 4:1 have much less room for error. My personal fav's are epoxies that are 1:1 ratios. The ratios should be the same for lam coat or hot coat, unless you are changing hardener (for example: from fast to slow). You don't really need two separate hardeners in a typical garage build. Fast epoxy is still waaaaayyyyy slow enough for a hand lamination. I like RR because I can get it locally quick and easy, the others have to be shipped and I swear they always ship hazmat slow. Essentially, they are all the same bulk resin and hardener, it's just the fillers that are different.