You have to ask what yourself what your goals are... I was in a similar position as you (almost completed a correspondence degree) and after alot of consideration chose to try the STA-21 route first. Got accepted on the first try and never looked back. If I had finished the correspondence degree and got right into OCS I'd be a LTJG by now...but those are some big IFs. Now I don't mean to slight correspondence degrees but the couple of cases I have seen they didn't get accepted to OCS the first time. For one friend it took three tries, for another friend (AF with a Master's) it took a switch to Chaplain after three years.
So I guess my advice would be to try STA-21 first. Why rush? You can never have too much education, you'll have a great time getting it, and those gold bars will still be there when you're done