The differences are mostly cosmetic, most of the parts are from the same bins, but a few things you should know:
The LE weapons are very similar to military in all respects - different barrel lengths, semi vs. full auto, but for all intents and purposes the same gun.
The Match Target name was arrived at to get around the states that have prohibitions on any rifle with the "AR15" name. If you live in one of those states, the sunset of the Assault Weapons Ban means nothing to you, and you still need a "Post Ban" gun. Likewise, the "banned" features are absent on the Match Targets - no bayonet lug, no folding stocks, no flash hiders - compensators are ok, though.
Differences that may matter to a greater or lesser degree to you:
On most of the civilian guns (except the 6400C/M4 semi) only the chamber is hard chromed. This was not done to save money - it's no harder to do the whole inside of the barrel than just the chamber - but to improve accuracy, as chrome plating does lower accuracy slightly. Full auto guns have need of a chrome bore, civilian semi autos much less so.
Also, (again excepting the civilian M4) Colt uses a plastic/lead filled buffer instead of the military aluminum style. Some report it works fine to high round counts, some say it's junk. I'd change it, as I like to be as close to GI as possible on this kind of part.
Fire Control Group Pin sizes on Colt's Civilian line are larger - .170 so as to preclude installing M16/full auto .155 inards. Of no importance, just order any spare parts accordingly. Front push pin is and has been standard military for several years now. Plastic butt traps on some MT rifles.
Colt's big advantage is better quality control on machining and materials - and simply less problems, period due to experience - being the actual developer/producer of the weapon for the military since the begining. Ask any of the big training facilities who has the most trouble free ARs and the answer will always be "Colt".
Warmly, Col. Colt