If ease of maintenance are in your top criterion then you should very strongly consider an AK or FAL. After a lot of years owning, shooting, building, accessorizing, etc virtually every military style design I can say without any reservation that these two stand out as the easiest to work on and maintain. The only tool needed for the FAL (outside of a barrel or locking shoulder change which is a depot level repair) is something with a flat edge (rim of cartridge, knife, screw driver, coin).