The Sea Inside and The Diving Bell and the Butterfly are both about quadriplegics, and yet they are quite different.
The central characters in both stories are only able to do what others do for them, aside from communication. However, Bauby's condition is significantly worse than Ramon's. Bauby can't talk, and he has to communicate only by blinking his left eye. On the other hand, Ramon can talk fluently, and he can even write with a pen in his mouth (somewhat).
Also, Bauby's face is pale, one of his eyes is sewn shut, drool dripping from his mouth, and his mouth and nose damaged. Ramon looks just like he did before his accident besides some balding.
Both Ramon and Bauby have sarcastic personalities. However, Bauby isn't able to crack jokes, because they lose their point after blinking it out.
The purpose of the stories are also quite different. The Sea Inside's point is obviously to convince people that suicide should be legal, at least for quadriplegics. However, the point of The Diving Bell and the Butterfly is much harder to understand, as I explained in an earlier post.
In my opinion, The Diving Bell and the Butterfly is more powerful than The Sea Inside. It seems more heartfelt than The Sea Inside, as it was Bauby's way of communicating with the outside world. It wasn't necessarily trying to sway the reader's opinion.