I have been on again off again shopping for a M4 upper to go with my M16.  

My M16 has an original 20" pencil barrel upper.  I have started to really like the weight and feel of original A1 uppers, triangle handguards and all.  I have a aimpoint on a goose neck off the carry handle and it works out fine for plinking.

I still have a urge to get a 14.5" barrel just because I can do it legally.  All the flattop uppers that I find are $800 to a $1000.  I like the looks of the flattop with the Aimpoint mounted forward, but $800 is a decent chunk of change for what you are getting.

What I am wondering is what is all the fuss over the short barrel uppers?  Are they really that much handier than a lw 20" barreled upper?

Knowledgeable Comments appreciated

In close quarters they are definitely handier but of course the trade off is slightly slower velocities.  I have 2 M4's and love them both but I wouldn't want to depend on them at ranges over 100 yds if I had a choice of them vs. your 20" version.  It really depends upon what your primary use for the weapon will be.