I tend to find most of them unlistenable - having a good "radio voice" is important to me as I listen to a lot of speech radio on the BBC, and it sets high standards. Though there may be better content-wise, in terms of production, professionalism, and general "sounds like a real radio show" stakes, I tend to enjoy the Mac Observer's podcast. Most of the others I've listened to seem unplanned, uncharismatic, and just had me switching off within five minutes.
None of the Mac ones are anywhere near as good as TWiT though. It's an amazingly good podcast, and with most of the presenters being Mac-savvy and covering the Mac quite extensively, you could do a lot worse than listen to this for your Mac podcasting needs.