From Boston, the best value if you want to enjoy a nice long haul is going to Asia IMO. Both Cathay and JAL fly direct from BOS to HK and Tokyo respectively from where you can connect to anywhere in Asia for 50/55K miles each way in J depending on where you go.
Europe? Meh, much of that continent is only 6-7 hours from the east coast (I'm happy with economy for 20K off peak each way) and it's freezing cold right now. And the oneworld business class products to Europe are either so-so or a fuel surcharge minefield (BA). Just my two cents.