Ok, so if I wanted to build a carbine for fun and the occasional under 150 yd woodchuck and other vermin killer, which should I get? Hunting accuracy is all I need...

chrome lined.

WTF is chrome moly anyways?  Everybody sells it but other than not chrome lining what makes it special other than steel?

Chrome moly or chromium molybdenum is simply referring to the kind of metal the barrel is made of.  Almost all weapons use some form of chrome moly metal, from AK47s to FAL and ARs.  Most non-stainless steeled barrels are chrome moly barrels.  

Chrome Lining is an additional process on top (or technically, inside) which adds a hard layer inside the barrel.  This hard layer resists pitting, rust, and increases barrel life.  It is what I'd recommend to get on a non-stainless steel barrel.

On the flip side if you get a chrome-lined barrel with a poor chrome-lining it will reduce the accuracy of the rifle.  Most reputable companies will deliver a nice chrome lined barrel.  I personally have always used bushmaster barrels and I have been very happy, you should also look at Rock River Arms and Stag (if you want a budget minded setup).

At 150 yards a 10" barrel is still very accurate, the 14.5-16" M4 barrel would do well, as would the 16" HBAR.  

Really, just get a gun from a decent company, add some optics, maybe a new pistol grip, and you are done.  I'd say a flat top M4 with an IOR scope would be awesome, don't worry about free-floating barrels at that distance.

I went with a RRA ss middy so I could have fun but, still have the accuracy for shooting yotes which is what we mainly do.i  

for under 150 you won't really notice much of a difference between Stainless and chrome lined in terms of accuracy...

sub MOA is possible with most major manufacturer's Chrome lined barrels...

I hold sub moa with both my Sabre barrels 16 and 18" both chromed...  

I havent taken my Del-ton kit out to try yet though =)