I have a Magellan Merridian Marine but it's the only one I have exp with so don't know about the others. It was a little bigger then the others and had a marine database. Look into one that has extra space available to download more info, I need another memory card to download any extra stuff.
Also check with Vanns.com before you buy, mine was about $100 cheaper from there compared to anything around town.
Good Luck