Speaker shootout question -- do you position the same or differently, depending?

If you're comparing two speakers at home, do you position each the same or do you position each as (roughly) optimal for that speaker in your room?

I'm comparing a tower and a bookshelf now, and their design is different. It would seem that the best way to compare would be to figure out what is optimal for each and then compare them in (likely) different positions. 

What kind of process do you use for comparing two differently designed speakers?