Each of the fancy names is just different rifles with different options. It might help to ignore the names and first figure out how you want your rifle configured - bbl length (20", 16", 16" m-4 style), type upper (A2, flat top, UTE - Rock River's elevated flat top with built in iron sights), and type buttstock (standard A2, Short entry, or collapsible). There are a few other options too but those are the basics. Once you decide what you want on your rifle, then compare their different models and see which one matches.
From their pics and description this is what I gather:
Entry Tactical - 16" M-4 type barrel, flat top upper
Tactical CAR UTE - 16"HBAR, elevated flat top with iron sight
Elite CAR - 16" HBAR, flat top upper
Elite CAR UTE - 16" HBAR w/ mid-length handguard, elevated flat top upper with iron sight
Elite CAR A4 - 16" HBAR w/ mid-length handguard, flat top upper
CAR A2 16" - 16" HBAR, choice of standard CAR or mid-length handguards, A2 fixed carry handle upper
CAR A4 16" - 16" HBAR, choice of standard CAR or mid-length handguards, flat top upper
Standard A2 - 20" HBAR, A2 fixed carry handle upper
Standard A4 - 20" HBAR, flat top upper