Which barrel is better the standard chrome lined or stainless steel barrel pros and cons?

General chrome lined lasts longer, but stainless is more accurate. This is a generalization. A poor made barrel is a poor made barrel, it won't be any more accurate if it's made out of stainless.

It depends on what you plan to do with said barrel.

I just started getting into ARs last fall. I built my first myself and have standard black 223 Wylde (which is safe for 5.56 also from what I understand) and just ordered one for a guy who wants a stainless 223 Wylde.. Basically if I shoot it a lot I'll be better off with the one I have?

There is a third alternative that may provide a better combination of features than either of OP's choices.

That would be a 4150 CMV steel barrel that is NOT chrome lined, but rather is QPQ SN (nitride or Melonite) treated.  This provides much greater hardness and corrosion resistance than either stainless or chome lined, yet leaves the rifling unaltered (unlike chrome plating).   This process, done on a good barrel, will last much longer than stainless, and may rival the life of chrome lined barrels, while providing better corrosion resistance and a hardness that is over the entire surface of the barrel, not merely the bore.

Also, even national championship bench rest shooters of stainless barrels are sometimes having them nitride treated to extend barrel life.

Just wanted you to know that there is a third choice and that in many instances it would be a better one that stainless alone or a chrome lined barrel, depending on how you intend to use the rifle.

I agree, they are all I'm buying anymore. My Voodoo 16" middy is fantastic and I just ordered Faxon's version of the same thing to try.

This. I don't see the point in SS barrels anymore since QPQ/Melonite/Black Oxide/Nitrocarburizing/etc has come on the scene (for the reasons mentioned above).