'Break In' is the same for all barrels, chrome-lined or not... It's a process of shooting & cleaning that is supposed to wear off any 'rough' edges of the barrel throat...
In the end, the question has more to do with 'what will the gun be used for'....
Some of us will never take our AR to 'the boonies', and actually DO care about that extra 1/2" at 100yds...
For that case, CM (or better yet, stainless) is best...
However, for a rifle that will be rolling in the mud, et al, chrome is better...
It all depends on intended use, but unless you live in a corrosive environment (such as near salt water), or take your rifle sloshing thru water/mud, you don't need chrome-lining...
If you do any of the above, the situation is different... Chrome-lining is also a plus on machinegun barrels that will be subjected to repeated mag dumps, etc (for thosw who see the purpos of owning a MG in being able to rip thousands of rounds down range at 'minute-of-backstop' accuracy, as fast as possible)
Oh, and almost any barrel will outlast your use of the rifle, unless you are (A) into CMP/NRA matches, or (B) wreck it by poor maintanance or overcleaning. Chrome-Moly barrels have been recorded as 'still shooting' after 30,000 rounds....