@Hundstrasse
There are some minor differences between the GameGear and Master System versions of JP. I would say the Master System one is a harder game, mostly because the Raptors deal more damage and move a lot faster.
Some screens have a couple of differences, again, most of those I noticed on the Velociraptor stage and the boss for that stage is much more aggressive.
I would also say the similar things about the NES and Gameboy versions, the NES version is harder as enemies move a lot faster, Raptors are incredibly aggressive, but can be foiled by doorways.
The GB version has a harder T-Rex encounter, just because you need to focus on ammo management, saving all your non-standard ammo.