As far as one being better than another, I wouldn't really worry about it, as most if not all of the ones you will find available now have been through one or probably more arsenal rebuilds, in which interchangeable parts were used, without a thought to future collectability.
The older models will have flip rear sights, push-button safety, and front band w/o bayonet lug. There are two bolt variants, round and square.
Get one while you can, and shoot it! They are a blast to shoot, low recoil, and lightweight.
Quite right. It would be difficult (spelled $$$$) to find an original Carbine, with all of the proper parts, codes, etc., that actually is original.
It has become a popular sport to take complete Carbines, strip them, then hunt-down parts that were correct at the time of manufacture. The gun is not authentic, but it looks original.
I have a Quality Hardware, with '42-dated Rock Ola barrel, but just about every other part appears to be of the latest configuration, with round bolt, M2 stock, bayo lug, etc.