I am a fan of Garmin units. I have looked at a number of brands (Raymarine, Garmin, Lowrance, Northstar, etc) and keep coming back to Garmin as my favorite. Plus, they have the best bang for the buck, IMO. I also prefer a single screen, in part because that is what fits my boat best. If I had a different layout the the $, I might consider multiple large screens.
Garmin is generally regarded as having the best, easiest to use chart plotting GPS devices. They are easy to understand and use. They do use Garmin-proprietary BlueChart or BlueChart g2 charts, but I like them. As far as getting "stuck" with them, amny brands of plotters only support one 3rd party brand anyway so you like it or you don't.
Garmin's strength is chart plotting, and also provides good sonar and radar, and very nice XM Weather. If your priorities are fishing or radar, there are other brands which are better than Garmin. Garmin's larger "networked" units will let you overlay radar on the map and split the screen into two views (or more depending on the model) so you can have multiple views up. I use this all the time when fishing.
Before deciding on a unit, I would strongly suggest looking at the new networked units Garmon is introducing in the spring. They have a totally new interface and many new very interesting features such as satellite imaging overlay and an uderwater "fish eye view". I was these units at the NY boat show and they looked OUTSTANDING. Very clear, bright screens (as good as or better than Raymarine E-series); crisp images; intuitive to use; great detail. And they are priced very well - roughly the same SRP as their current units - which is lower than the competition - with a better feature set than the competition. Garmin has really stepped up their game. Sizes are an 8" and 12" screen.
I probably sound like some raving Garmin nut (or employee), but I just think they have a really good product.