I am curious what the big differences are between the various grading companies that are available like: BCCG, GemMint, PSA, etc?

Is one considered better than the other?

I believe PSA and BGS are the standard bearers.

Welcome to SCF...Quick run down.

In General, Company/Main Area/also the order I use for my own cards:

SGC= Pre-war
PSA= Vintage
BGS= Modern, Bccg is bgs's flythrough, not as stringent, most cards are ~2 grades lower

GAI= Was ok, but is now defunct. Hard to say what transpired with some cards / packs now(speculation, maybe...but they gave the reason by their own actions)

They all make mistakes(to err is human), grading is subjective, but the 3 I listed are fairly solid across the board.

The rest..Besides Canada's KSA, Stay away..far far away!!