I use regular Food-Grade Parafin wax with some teflon powder mixed in. Only get flakes after the first ride, and they brush right off using a soft-bristled paint brush. No build-up on the cassette.
Are you working the freshly waxed chain free before installing it? There is a video with this Aussie fellow demonstrating his waxing technique, and he slides the chain around a wooden knob before installing it. This not only loosens up the chain a little, but it knocks off some of the unneeded bits of wax before the install. He does this at about 16:01 on the video. Here >>>