The two best units sold today come from Humminbird and Lowrance. Humminbird has a slightly larger margin of the market. People are pretty divided into preferring this or that based on personal preference of how it looks, how they feel they can operate it, and such.
CHIRP sonar is the new standard and MEGA the best of the best. Ultimately it comes down to your own personal preference. I prefer Humminbird as the menu screens are all under the same section so adjusting settings for me is easier there. Humminbird also offers a few features like the color bar that other makers leave off. The color bar presents all available colors in a particular color palette on the sonar screen so you can always tell whether a echo return is soft or hard and where it falls along the rainbow.
Best thing is to get lots of advice and read all your can. I suggest going to the major makers and actually pulling up the manuals and reading them. After all, that is what you will need to see to know how user friendly the units are.
I suggest avoiding Garmin.
AS far as mapping, Humminbird Lakemaster only works in Humminbird. I prefer Navionics, I like the way it appears on the screen. It is a one time purchase, no updating for lakes is really necessary ever.
Capt. Craig Copeland
Licensed by the US Coast Guard
2013 Nautic Star 2110 Shallow Bay Boat
Humminbird HELIX 12 CHIRP MEGA SI GPS G2N
Nautic Star Boats Pro Staff (nauticstarboats.com)
Redneck Fish'n Jigs Pro Staff (redneckfishn.com)