Anonymous 07/15/2017 (Sat) 15:32:28 No. 10921 del
Not technically ports, but there's the significant differences between Virgin's version of Aladdin for the Mega Drive and Capcom's version for the SNES. There's also the absolute clusterfuck of bonus levels and graphics changes that Earthworm Jim was subjected to:

If you can find a copy of Retro Gamer they sometimes do comparisons between various home computer versions of whatever game they're highlighting that issue which really highlight how little of a shit game publishers gave even back then.