Jerry, Generally if you order from D* you'll get whatever they have in the warehouse at the time.
The HR20 has an OTA tuner in it, the newer ones don't.
If thats something you need (I do) I would call D* and have them replace it and they will send you a new HR20, if you don't need the OTA tuner, then it doesn't matter which one you get.
only differences are pretty much slightly larger hard drive size the newer you get.
300-320-500G one other thing, if you get the HR23, you don't need the BBC's, thats about it.
I have been using the HR20-700 for years now, but like I said, I need the OTA tuner, so thats what they ship me when I need one.
I've added an External Hard drive to mine (1.5T) so the hard drive is not an issue for me.