lakemaster is cheaper and not much difference between the 2 brands i can tell

Quantity of lakes covered/level of coverage
Updatable or static?
Satellite overlays/panoramic photos or not?
Community Layer/User Generated Content or not?
Ability to add new uncharted lakes yourself by recording and uploading for free.
What features does Humminbird allow you to use on either product - I.e. pool level adjustment?
Compatibility with other brands of plotter?
Ability to sync data with mobile devices/computer?

Etc.

I'd say there's lots of various pros/cons between the two.