I thought Standard would be cheaper...it turned out Prime was, although in my case, I have a special-needs family member that lowers the premium.
I got the best of both worlds: Prime, so no deductible, and almost no co-pay, and yet, they let us go with a local doctor because the closest military facility is over capacity with retirees.
Yet, when I need the ER one night, I could still go to the base!
I too had no idea what to go with in my last year on duty...check carefully. I'm extremely happy with Prime.
On the other hand, United's dental and vision plans were far superior in coverage, premium, and co-pay.