If you already have something in 5.56 or .223 go with the AR-15. AR-15's are really cheap right now. The market was saturated and now the manufacturers are selling them cheap. You should be able to pick one up for about $800. The ammo is still a little easier to get for the AR it seems like as well.
"If ye love wealth greater than liberty, the tranquility of servitude greater than the animating contest for freedom, go home from us in peace. We seek not your counsel, nor your arms. Crouch down and lick the hand that feeds you; May your chains set lightly upon you, and may posterity forget that ye were our countrymen."
Samuel Adams
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