When shopping for an AR which chamber is prefered, 223 or 5.56?  And if it isnt too complicated, please educate me as to why one is better than the other.  thanks!

I belive the 5.56 is in the thousands of an inch larger, and hotter.

the 5.56 chamber is a wee bit larger than the .223

you can safely shoot 5.56 AND .223 rem in the 5.56 chamber

it is NOT adviseable to shoot 5.56 in .223 chambered rifles (excessive pressure potential)

I think the ARFCOM FAQ's address this.

It's not that the 5.56mm is "larger" it has more "free bore" then the .223 chamber.
www.fulton-armory.com/556-vs-223-Chambers.htm

If we are talking about .223 Remington SAAMI-spec chambers in an AR15, OH NO!

Do NOT use such a chambering if you EVER plan on shooting any military NATO 5.56 ammo, which happens to be only the most common, least expensive and most widely used AR15 cartridge available in all the world. In other words, NEVER buy/use a SAAMI-spec chamber in a battle rifle, especially if the barrel and chamber are chromed, as you cannot fix it!

Here's the problem. Many NATO cartridges have bullets that will become jammed into the rifling of a SAAMI chambering (the throat is too short). This is VERY DANGEROUS, for a grat number of reasons.

Fulton Armory uses a "5.56 Match" chambering in its rifles/uppers/barrels (in fact our barrels are marked as such), which is a slightly modified SAAMI chamber with a tad longer throat to accommodate NATO bullets. The Fulton Armory 5.56 Match chamber allows for the safe and reliable use of all SAAMI and NATO ammo, while offering the accuracy potential of the SAAMI chamberings with match commercial cartridges. Remember, there's often a large difference between bolt guns and military rifles. This particularly true for the 5.56 vs .223; Fulton Armory is well known for the finest performance for any given platform, and our 5.56 Match chamber is one way we achieve that performance with the AR-15-type rifle.

Thanks for the info.  I will probably get most of my ammo at gunshows.  Sounds like the 5.56 chamber and surplus ammo would be the economical way to go.  

5.56 chamber eats anything.

You could get a Wylde chamber, which is in between.