your choices in and out of LEX are limited.

Since I avoid USAriways like the plague, and always regret it when someone convinces me to "give them another try", I reccomend against their program, especially out of LEX, where they have caused me nothing but trouble.
I'd say Delta is your best bet, although their program currently is terrible for the low fare flyer. I forget who else flys out of LEX. You would need to tell people a bit about your flying habits to help us give you the best information.