Like BoBo I have a old Eagle 500C on trolling motor that still works great and just installed a Humminbird 998. I like both. Like Duncan said hands on at the counter will help. In just plain 2d I don't think you could beat the Garmin 500 or 550c. Figure out your budget first then look at units in that range. Pick a couple then ask questions. Plenty of people on here will have experience with about anything you chose. My recommendation is Color screen and GPS either brand and you should be happy.
By the way Duncan just got rid of my FLH. If I could I would go back to my 1987 FXLRC. Best bike I ever owned.
Proud Member of Team Geezer
Charlie Weaver USN/ENC 1965-1979