It's been posted before but they all can do the same thing "except":
What would be interesting to see would be a side-by-side feature comparison of the various models, from HR20-700 to the latest HR24. How do they compare in command response, channel changing, HDMI compatibility, hard disk size, supported modes (whole house, 3D, OTA), etc?
Maybe this exists here someplace, but I don't seem to find it. Maybe this would make a good "annual report."
HR20 has OTA, but can't handle 3D.
HR22 change drive size to 500 GB [from 300 earlier].
HR24 has internal DECA.
Speed seems to be:
HR21/22/23 are the slowest.
I may have missed some here, but these seem to be the major differences.