Well this is very general, you'll want to define your uses and do some research but in a nutshell:
A stainless barrel can be very accurate and easy to clean. I think most come in 1:8" twist which is a good compromise for most 5.56/.223 ammo.
Chrome-moly unlined barrels are the cheapest and can be very accurate but harder to clean. They may have extraction problems unless you keep the chamber clean. Most come in 1:9" twist which may not work well over 100 yards with the heaviest/longerst ammo.
Personally I'd rather have a chrome-lined CMV 4150 steel barrel or full milspec steel. Stronger and cheaper than SS yet still plenty accurate for most uses and at a decent price. Most people go this route and you can find 1:9" and 1:7" rifling twist (chose the one that works best with the ammo you'll be using).