So I'm slowly figuring out which AR I want to buy. This will be my first AR.  There is not anywhere near me where I can rent an AR to shoot to help me decide so I will rely partially on your opinions.   I am pretty much set on Bushmaster - and their 16 in heavy barrel, A3, flash supp, and tele stock.  I plan on adding a vertical grip and optics, possibly a light but don't want to overkill.  I looked more closely at a 20 in barrel this weekend though and am undecided.  Even though the 20 in is better at long range shooting (accuracy, velocity, etc) realistically when am I going to shoot 300 plus yards plus?  200 yards is the fartherst common range distance near me.  I doubt I would get into the long range competitions.  CQB shooting seems like a blast though.  Also, the 16 in would be better for home defense in my eyes and more fun to shoot.  Prices around me are roughly the same for either at appx $900 with A3, case and one 30 round mag.  

Please throw any ideas or comments my way before I drop a wad of cash.

Thanks.  

Buy the carbine now, then get a 20" (or 24") upper later. The only real difference in barrel length is going to be velocity; I don't think accuracy is going to be affected to the point that you would notice the difference.

Ck out DSA new ARs they are built one at a time. as they get ordered very accurate.
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Sounds like you have already made your decision.  Just buy one and start shooting!  You can always add a different upper - 16" or 20" later.  There is no accuracy difference in barrel length until you reach really extended ranges.  The 16" barrel is louder than the 20".

Quoted: Please throw any ideas or comments my way before I drop a wad of cash.

Buy a model with the Lightweight or M4 profile barrel - you will be glad you did.

Why would I prefer a M-4 barrel over a heavy barrel? Is the main reason weight? From my reading/research I heard/read that the heavy barrel is better for more sustained firing but is slightly (1 lb) heavier. I also saw that a regular bayonet does not effectively mount to the carbine - but this is not a big concern for me.  If out of ammo I would drop my AR and draw a sidearm long before I started using a bayonet - even though that would never happen (hopefully).  

Read the Ideal Rifle

If you're really planning on mounting optics and a light, get the lighter barrel.  We measure weight savings in ounces - a full pound is waaaay beyond slightly heavier!