Just wondering if anyone has any thoughts/suggestions on which direction bikes should sit on the roof

I've Thule bike carriers which can be left or right opening.

So do I place both bikes facing forwards, or do I have the bikes one front facing, one rear facing?

If the answer is simply try it and see, so be it, just wondered if anyone had experience of whether one option is easier for mounting the bikes, or provides less wind noise etc.etc.etc.

cheers