Welcome to My Fishing Pals. Glad to have you aboard!
I purchased the Helix 10 this winter and had it on the water for the first time over the opener. I got the Lakemaster chip. From previous experience, I used to have a Garmin with a Lakemaster chip also. I have yet to NOT find a lake. BUT there are differences between the Navionics and Lakemaster and most of this is going to depend on what exactly you are looking for. I suggest you do some research on both. I purchased Lakemaster for the i-pilot. Last I heard, the Navionics card could not follow contours, but I might be wrong about that. I do know that Navionics seems to be more interactive with the ability to upload new data that is posted by user... not sure on exactly how that works.
You might want to check out the lake lists of both and figure out whether your lakes are listed or not. Unfortunately, it seems you need to email Navionics to get their lake list. Following link is for Lakemaster...
Even eminent chartered accountants are known, in their capacity as fishermen, blissfully to ignore differences between seven and ten inches, half a pound and two pounds, three fish and a dozen fish. ~ William Sherwood Fox, Silken Lines and Silver Hooks, 1954