It's really a bit of preference.
The 13/64 file gives a bit more hook, which will perhaps give better or more aggressive performance, but perhaps also might wear out faster. I say perhaps because I have never seen hard numbers one way or another, and even trying both I haven't really found that much of a difference.
With some file guides I find the 7/32 doesn't make enough of a hook and winds up leaving the cutter sort of "open", especially if you look at it from the outside of the cutter. This is fixed by just making sure that your file is sitting as low as it can when you file, however.
As you wear the chain back the overall height of the cutters above the tie straps goes down. A lot of people make the argument that it makes more sense to use 13/64 later in the chain's life, when the cutter is shorter and may benefit more from a smaller file.