There is no difference in accuracy between the two brands.
Garmin seem to have deliberately targeted the reccy user for some years now with pricing.
Magellan seem to have gone after the professional with technology.
Nothing wrong with either tho... kinda like Euro phones versus Asian ones.
They each have a different feel on menu layouts etc but will do exactly the same thing in the end
I'd buy whichever one you get the best deal on that suits budget and your personal likes.