I use the 5 squares per inch--seems perfect. Actually what I've been buying lately is this stuff from Office Depot/Max or one of those anonymous chainstores, booklets that have 5 squares on one side, 4 square on the other. I'm starting to work on a really large dungeon now, and want to get something much larger than 8" x 11.5" however.
Speaking of Office Depot, ever have players assume there are places like that in your campaign where they can go buy whatever magic item listed in the DMG (not to mention whatever whizbang new item mentioned in a 3rd party booklet)?