It depends on your destination. For instance, I only fly TATL and I like to sleep in coach on the overnight outbound and then enjoy a nice daytime business class flight on the return home. This is impossible to book with Delta for dollars, you used to be able to at least book it this way using miles but that too went away this year.
I went to the Air France website which allows you to book different fare classes for each leg and I got a 399 coach flight to my destination non-stop on Delta metal and a 1200 flight returning home also on a non-stop on Delta metal.
So basically, try and use Sky Team partners to book flights in different fare classes for each leg of a RT TATL.