Have used both Jack Martin and IMIS as brokers[neither is the underwriter] - both were great to deal with [however never had a claim with either].
The big factor is if you are truly going to get full time cruisers insurance. In that case IMIS is the only one who offers the Jackline which is a truly unique policy designed for the full time couple cruising anywhere. I would encourage you to write your policy now with whatever company so that when you leave the Chesapeake you just have to change cruising grounds. Most US carriers will not cover you outside the states and the international ones won't cover you in the states. So much fun.