As an educational tool the Raspberry Pi might be the best.
Especially the new version with a quad core and four USB
ports. A couple parts of the pandaboard are binary blobs and the
underlying hardware is undocumented to the public.
The raspberry-pi does have some undocumented bits.
These are well supported by insiders with full NDA documents.
Someone should say something about price.
The R-Pi is inexpensive enough to have two.
One to develop on and the other to test on.
For both you do want a powered USB hub for
keyboard and mouse. You do want a couple
spare uSD memory cards and a USB card reader
or way to read/write/repair the contents of the memory