Ahhhh Larry, you may want to recheck on your Delta and United info. If not mistaken, both have to go through other airports (Delta = SLC and United = Denver). Southwest goes through Phoenix. Although they may have direct flights (with a stop), I would think that for this time of year Phoenix would be a preferable stop over the other two due to weather this time of year? But only if Southwest has a direct flight through Phoenix (no change of planes).
Just some food for thought. Air Cargo is definitely the way to go though. Oh, also watch the arrival times. I had a shipment arrive on a flight into OKC on United AFTER their cargo terminal was closed for the evening and they refused to let us pick them up that night. We save the koi the next day....barely.
Steve