If you're travelling small is good - Garmin Pilot III or GPS92 (no moving map) is good. The Pilot eats batteries faster than the 92.
You can download the database of your choice online for $35 from Garmin and swap between areas at will. Software updates are free.
If the unit has a basemap, that will not be changeable - so buy the area you fly most often and live with the downgrade when travelling.