If you want to have both markets, they're in reach.
If you want to go after 'as many as possible', then go big. In the attic, I'm thinking Antennacraft HD1850... but it's long and wide, 15' long and just over 9' wide. As you go down in size, you reduce your hope of seeing the Low-VHF signals... If you can fit them in your space, use one for each market and cable them separately to to each TV.
http://forum.tvfool.com/showthread.php?t=2882
If you change your mind about attic mounting, the Antennacraft is fairly easy to refold without damage. If you chose to mount outdoors, the Winegard HD7084 would be another option... it has a reputation for being more difficult to refold though.
If you aren't inclined toward 'every possible channel', there are quite a few alternatives that depend on what you 'must have'.