One would think a dynamic on top and a condenser underneath would be the most logical thing, but I've actually had some good results from doing it the other way round. When I consider I would normally EQ in a bit more crack into the top mic and then tame the harsh crackle of the bottom mic, it actually makes sense to try and balance this out in the signal chain by using a slightly brighter mic on top and a battered up '57 underneath.
Most common thing is just a 57' on top and bottom though.
Always remember to flip the polarity!