Well, it depends for which companies you can redeem your points.

However, LHR doesn't seem such a good option, since you would need to have an additional transfer in Zagreb (ZAG) or somewhere else in Europe.

If you can get an Austrian Airlines ticket, it might be good to fly to VIE and then directly to DBV. This seems to be a daily route especially in June.

LH / OU fly FRA-DBV, too. OU is a Regional Star Alliance member so you can get this ticket through LH, as well. I think LH / OU have daily services on this route.

And finally, if you prefer flying via FCO, there is a direct OU / AP flight nearly every day to DBV. And you can fly AZ, DL or AA to FCO from JFK.

Hope this helps...