I have been growing Hoyas for 15 years and my mix is usually

50% potting soil

25% perlite (prefer the larger chunky kind)

25% orchid mix or coconut husk

The trick is to have a fast draining mix.

I suspect a lot depends on the Hoya, but what ricfl uses it basically identical to what most of mine are in. My bella and multiflora are in much more water retentive mixes, since they flip out if they get too dry. I am considering putting my carnosa compacta and kerrii types into Al's gritty mix to help save them from overwatering. That one is popular on the succulent boards, composed of crushed granite, fine bark, and turface.