DVD, with some reservations. Cathe's DVD's, especially the Intensity Series, are excellent: good chaptering (except for the earlier DVD's, but the sound and picture quality makes them worth it anyway), excellent premixes in the Intensity series and BB Series.
The reservation I have is that many people seem to be having problems with the BB DVD's playing on their players. And newer players seem to have more problems than some basic players. I personally have a cheap RCA, one-disc player, and aside from a longer pause than usual when there is a layer switch (though SNM has not replied to my question about where the layer switches are, though I've asked several times), I haven't had any problems.
Do you already have a DVD player? If you're thinking of the BB series,, you might want to ask if anyone with the same player had the problems.