Personally, I'd stay away from pinned 14.5" barrels, due to the difficulty in changing out the muzzle device.
I'd suggest a 16" midlength upper in 5.56 from a quality company, standard lower with a good LPK (nothing match grade, but a solid milspec trigger), full auto bolt carrier, handguards and stock of your choice, and ammo. Add either a detachable carry handle or rear BUIS and a quality optic of your choice, and shoot the crap out of it.
For a first AR, though, I'd suggest learning on iron sights, and adding the optic later on. Reduces up front cost, lets you learn the fundamentals (what good is that red dot if it fails and you don't know how to shoot for dick with irons), and you can use the money saved for ammo and training.
Palmetto State seems to be the best bang for the buck right now. You can get a complete DIY rifle for under $600, or a complete rifle with Aimpoint PRO and Magpul rear BUIS for $1,000.