I'll chime in here as well.  Looking back through my numerous copies, here are some of my observations:

Folio maps are larger.  High quality maps.  Seem to have used a thicker paper stock and medium gloss.
Early boxed sets can have maps that are too big for the box.  Quality is similar to folio but paper stock does get thinner.
Boxed set maps have a range of gloss, mostly a higher level than folios.  Later boxed sets have smaller maps, some non-glossy.

Mars' posts pretty much sum it up, although I'm sure there will be some variation due to how the map printing runs were handled.