I suppose that my reaction would be to select the most convenient non-stops (if there are any), then comparing pricing between Y and F. Often (and STL's increasingly limited service and the higher prices flowing from that as time goes on), the cost/benefit of the price difference would outweigh the perceived benefits of First Class on that short a flight. On the equipment likely to be encountered and with the limited services for F pax, getting there and back quickly would mean a lot more to me than a 'cheap' F ticket requiring me to change planes in ATL, etc..