the bigger bang for your buck will be in the hubs!
after that it will be in the rim and build.
are you climbing hills go for shallow and light.
If you are doing a bunch of flats then get deeper dish hoops.
If you are a power smasher then get a supper stiff wheel build.
I had stiff wheels and went to aero. I lost on the climb and gained on the flats. it was a wash.
then I went 38mm carbon, and I gained on the hills and the flats.