IIRC, there were nine manufacturers under contract to produce the M1 Carbine. A previous poster listed some of them. Ones not mentioned were Underwood, IBM Corp., Irwin Pedersen, Quality Hardware, and Std. Products.
Irwin Pedersen made the fewest, and not coincidentally, now command the highest prices, if correct.
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.