The biz class decision is more than just the flying time. You have made the journey and arrive well rested and stretched out. As soon as you hit the ground you are ready to go. Plus you spent the 24 hours together dining and experiencing nice service.
Getting an open jaw with either Emirates of SQ would be my choice. I always do open jaw flights into Europe and take a train journey in between.
For the train journey consider:
European trains depart/arrive from the city centres.
Airports, you need to first travel out of the city, to arrive 2 hours before your flight, security, etc. The actual flying time. Then arrive, luggage and transport to the city. So thinking hotel door-to-hotel door it might be 7 hours v 11 hours by train. European trains are reliable, very comfortable and well serviced. Plus you get to see things along the way.