Use a sanitary cross when you want the waste/soil from one fixture to backwash to another fixture. Anotherwords, almost never.
If there is a decent length of pipe between the sanitary cross and the fixture, the backwash isn't SO much of an issue.
A double fixture has a longer radius on the sweep of the fittings, thus, it tends to direct the waste down the vertical instead of across to the other fixture.
Don't count on either to properly direct a snake cable downstream, even double wyes are famous for allowing a cable to jump across.