There are pros and cons for each direction. If you plan to spend time in Europe, an Eastbound cruise will get you there well rested and ready for sightseeing. Alternatively, if you have to go right back to work after your cruise a Westbound cruise will take you home without jet lag.
One of our favourite cruises is B2B Mediterranean and TA home. The Mediterranean cruise is port intensive and quite tiring, then we can relax on the TA.
One way air fares can be expensive, so look carefully for airlines that charge half of the return fare. Iceland Air is one to check among others. Also flights booked through the cruise lines can be very reasonable for one way.