For us, it has come down to reliability. We find that a mainline flight from the US to STT combined with RTFF has consistently gotten us to Roadtown more reliably than connections via either SJU or STT to EIS. IMHO, Seaborne is a huge question mark currently with its bankruptcy and subsequent sale to Silver Airways. Time will tell and we'll keep an eye on it to possibly try next year. Cape Air is far more reliable, but seats are more limited. For us it still comes down to a mainline flight to STT and RTFF to Roadtown.