AR-15

Colt AR-15

What is the difference between the Colt models of AR-15? There is a Match target, Sporter match, Sporter competition, Competition match target. I'm sure there are others. Also what colt model will be the most accurate out of the box, I'm looking at a Sporter Compition HBAR with a 20 inch barrel and a 1:7 twist. Would I be better going with an older model? ( SP-1 )