Are we counting minor (internal) hardware updates, or actual console redesigns?
For least number of updates, the Gamecube comes to mind: No hardware revisions (unless you count the Wii
) and I don't think there were even different MB revs. The original XBOX had no hardware redesigns either, but the MB and internals were updated through quite a few different revs. Does that count?
For most number of updates, the PC Engine had many, and even more if you count the Duo systems.
PC Engine
CoreGrafx
CoreGrafxII
PC Engine LT
PC Engine Duo
PC Engine Duo-R
PC Engine Duo-RX
And the PSP will have like 4 revs by the end of the year, heh.