We just booked United, IAD to STT, first week of May. Direct flights coming and going, so we will take the ferry from Charlotte Amalie to Road Town. We wanted a later departure time in STT, and the Spirit options were not workable. We found out Spirit was booking us separate flights instead of connecting flights, meaning we'd have to leave the terminal, get our bags, and then have to re-enter through TSA to make the second leg (in FLL). We tried going through BWI, but thumbs down on that return mess. When we added up the baggage costs, United wasn't too much more, and well worth the reduced hassle.