Well, there are 3 chart types really - Navionics. Bluecharts and Cmap. I haven't seen too many Cmap devices, so that's pretty much out.
Between Navionics and Bluecharts, I personally liked Navionics because of the larger coverage. However it looks as though Bluecharts do better in Bahamas - they use Explorer charts instead of the usual government stuff (and I read a few people complaining about Navionics being way off). In the end, though, I don't think any chart will ever be perfect, so that's just one part of the equasion.
I am leaning the Garmin way now (since I realized Raymarine makes you buy gps sensor separately - I think this is just a cheap trick on their part).