About Altered Beast, the Mega Drive port is said to play better. It also has added parallax scrollings. But at the same time it lacks some visual effects like when the screen turns grey during the boss fights. Like I said it was rushed but still good.
But there are plenty of ports which are better than the arcade, either on Mega Drive or other systems.
There are also plenty of people who genuinely enjoy playing home ports regardless of whether the arcade versions are better or not. Sometimes they just prefer how the ports look, how they sound... Sometimes the ports have additional content which still makes them worth playing in any cases... Some people might also prefer to play with certain pads/sticks rather than others... So many reasons... :)

