I hunt deer with an AR-15. Bear with an AR-10(well technically a LR-308 but the same thing really) works fine. Can't go wrong with a .270 though.
As to the AR questions, Stag is a good deal (get the plus package for an extra $100) however buying a lower and upper separately will save you some coin and let you get exactly what you want(or close to it)
Personally I'd stay away from RockRiver arms, Olympic, or Dpms as there is better value out there. Bushmaster has gone downhillsince being sold to Dpms, however Windham weaponry is the old Bushmaster and gives excellent value. You also can't go wrong with colt or armalite, however I steer away from them due to their political stance and anti-2nd amendment actions.
The main thing with AR's is that parts are interchangeable and easily modified, (read: expensive hobby)
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