Well, okay, I am a bit drunk and shouldn't be near the internet and so Asterix and Sonic are not side scrolling shooters. I just got a bit side tracked thinking about SMS games.
However, I would dispute your opinion that the PC Engine version is better. It has better graphics but is not full screen so when you play it there is stuff going on that you can't see, thus it is dangerous to be to close to the top or bottom of the screen. The SMS version is full screen and has excellent graphics (up there with Asterix and Sonic!) and so is more playable in my opinion. PCE version is nice though.