I think the similarities are far fewer than the differences, so I will start there. Both Aronnax and Nemo are well educated and well spoken individuals. Nemo might at times seem barbaric, but he is quite well spoken about it. Both men have an incredible love and passion for the sea. Nemo's evidence is the life he has chosen, and Aronnax's evidence is the fact that he has written books about it and is genuinely excited at the chance to study the mysterious sea creature thingy that is destroying ships. Lastly, both men are quite stubborn.
As for differences, well Nemo is a murderer. Nemo is also very secretive, and that bothers Aronnax. Aronnax is a scientist and scholar and believes in spouting forth all that he knows all of the time. He takes great pride in having people think of him as very smart.
For my part, I did not wish my intriguing and original studies to be buried with me.
Aronnax isn't saying he wants to go back to land to be with people. He wants to go back so people can hear about what he has learned. Nemo, on the hand, is perfectly okay with the rest of the world never knowing all of the things that he has learned about the sea and submarines. Aronnax has a deep desire to go back to civilization, and Nemo has a deep desire to never go back.