Well, as I understand, there are many classes out there, I have checked in internet and there are many classes out there but just some of the mentioned are on IWA or ISAF.
Chances are simple, FW, FE, Raceboard, RSX as I understand. I dont think Kona because if you are going to work a serious fleet, that class is not ISAF class.
Of the others, as people said, depends on your wind conditions really. FW looks lots of fun, but still needs updating equipment and high costs. Raceboard is a bit simpler on this, but for sure, someone racing FW wont like to race in a Raceboard and RSX. From this side, best thing can be FE but its more young guns oriented. RSX, can be same as Raceboard but Raceboard gives the chance to many people to buy (same as FW) some Used equipment and race for fun.