If you want Navionics, go with Lowrance.
Garmin has acquired Navionics but their graphs don't support them.....yet.
Both graphs will have similiar features. Sidescan, downscan and sonar.
Lowrance Elite TI series graphs will offer a touchscreen, FishReveal capabilities, Navionics support with Satellite overlay capabilities.
In my opinion, unless you have plans to run a Panoptix transducer for the Garmin graph, go with the Lowrance