All the USB does in most cases is creates a USB-Midi bridge, so essentially USB and Midi boards are the same. A lot of comps these days don't have a midi interface except for USB so check what your computer has.

However, some like the Line 6 KB series have analog/digital audio interfaces built in as well. That would be cool if you don't already have an interface for recording, and you want to record.

My advice...get the cheapest thing you can that sounds and feels like a piano. The cheap midi boards are really cheesy and plastic feeling keys. Look for a "stage piano" instead of a keyboard.

Ron