if you marsh fish, get the Navionics Platinum + for the Lowrance - IMO it spanks the Garmin for clarity and detail with Google Earth images. I ran that chip on an HDS 10 and it was impressive. Maybe run over to Breakwater Marine and get Derek to demo them for you.
http://www.breakwatermarine.com/ BTW, Derek knows (and sells / installs) all of these units and can fix you up. Good luck.