Are there big differences in maintenance/care between different types of clipless pedals?
Shimano pedals are usually brought up as a good beginner pedal because they are readily available just about everywhere, have several low-cost options, have standards that much of the industry follow for cleats and cross compatibility, and require little maintenance.  As you said, they don't get clogged up easily, but it can happen.  It just takes a LOT of mud.