Okay I do not have a Chart plotter type GPS I will tell you this up front. I do have a handheld Garmin which does about everything I need. I have however had more experience with GPS than most people. I have used survey grade GPS since 1991 and the secret to GPS has been and still is a clear line of sight from the satellites to the antenna. So the higher and more open you can get an antenna the better your stored locations will be and the better information you will receive period. The external antenna will be my choice if I do decide to get one for the simple reason I can mount it higher and reduce multi-path (signal reflection) the major cause of bad locations.

Plus I have said this before and most people laugh at me I would suggest you never use a GPS no matter what kind it is or how much it cost for it to be you sole mean of navigation. They can, for a number of reasons, miscalculate their positions at any given time and be a few feet to a hundred yards off. So everyone, please be careful how you use them.