Of the two choices (Stag or Bushmaster), I'd choose the Stag.
If you're even slightly competent around firearms, consider building your own AR rifle. Buy a stripped lower and buy a LPK (lower parts kit) and then build the lower yourself. It's easily accomplished in less than an hour if you take your time and don't force anything.
You can then buy or build an upper receiver in various stages of completion that fit your exact needs. You can make it anything from a home defense gun, to a door kicker special, or varmint rig.
I just built an AR from a stripped Stag lower and a Del-Ton upper. The other parts (rails, grips, sights, muzzle devices) are from suppliers like Magpul, Yankee Hill Machine, Rock River Arms, Burris, Streamlight and Blackhawk.
The nice thing about AR's is you can make them anything you want. You can build an entry level gun for around $600, or go all out and build something in the $1,500 to $2,000 range depending on quality and quantity of accessories.
Whatever you do, don't go out and buy every accessory you see for an AR. Figure out what role you plan on using the rifle for and then get your goodies once you see what works and what doesn't work.
Something that looks good on paper, doesn't always work out in practice.
