Right m8, I have alwaysed used Garmin, i have the Gramin 126 (GPS with internal arial) stright on my console, dad (cabin crusier) has Garmin 180 (chartplotter) ariel on roof, and we share the old Garmin 12 (GPS handheld), never had any problems at all. But I always considered Garmin to be a average suitable manufacture. For someone like me, on a (lose) budget who looks to buy cheap but good.
But the Navman with FUEL UNIT
sounds good, if keeping an eye on your fuel consuption is what you need (i.e. crusing lots etc). Navman have a good repuation, but as pointed out many people have had leakage problems and have had many units replaced. So if you want the added benefit of a unit that will be monitoring your fuel with the risk that it will leak (even if it does hopefully under warranty so shouldnt be to much hassel to replace).
Persoanlly I'd give myself a few more options than just 2, read a few boating mags to see what they say when they do a test, then decide what suits you.
well thats my thoughts anyway