The idea that blinking lights attract drunks is supposed by research to some degree, though what the research finds is somewhat more complicated than that.

Flashing seems to be more popular in the US, and solid-on seems to be more popular in Europe -- even to the point of being mandated by law in some places.

I'd say do whatever you want. If you have two lights, you're not likely to go wrong with any permutation -- two flashing, one flashing and one solid or both solid.

One advantage of flashing is that the batteries generally last a lot longer, so the light becomes more reliable, if you want to take that into consideration. Personally, I also like how a flashing light screams "bike!" where a solid light could mean a lot of different things.