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I am not a lefty, but I know lefties who use ambi standard AR's without difficulty. I imagine an ambi AR would have better re-sale value than a left hand dedicated AR, which might be something to consider.
Southpaw myself. I never needed a lefty AR in my life. If you buy one you will have a harder time selling it in the future if you choose to do so. Ambi controls is all that is needed. And for that you have lots of choices.