"Soundings" Good all-around.
"PowerBoat Reports" (like Consumer Reports, but for powerboats)
"DIY" can also be good if you like to Do It Yourself projects. It's a very good magazine, but I found most of it a little too advanced for what I'd like to tackle myself. But , I did enjoy some of the simpler projects.
"Trailer Boats" magazine has good articles on towing, tow ratings, trailers, etc.
For serious cruising, they usually like somrthing such as "Latitudes and Attitudes"