For photo transfer to presensitized board, I use drafting paper printed on a LASER.
In case you don't know what drafting paper is, or in case it might have a different meaning where you live... It is a matte translucent "paper" most often made of some kind of plastic. If you lay it on top of another drawing, you can copy it by tracing (perhaps could be called tracing paper in some places?).
It outperforms clear acetate sheets, as the toner sticks better on the matte surface and the diffusion of the light helps too.
A fairly rigid (thick) sheet is what I have had the best result with - the equivalent of at least 90g/sqr.meter (so somewhat heavier stock than regular copying paper (which is usually 80g/sqr.m).
Make sure to get a type that works with a LASER, so it doesn't curl up inside the very hot fuser.
This stuff works well as a diffuser for LEDs as well.