Originally Posted by GuyP
..I'm slightly swayed by the 298c's bigger screen.
I changed from a 178c to a 298c as my secondary unit. The increase in screen size is not really significant. One is almost square and the other portrait. I made the change because the 298c was (is?) preloaded with the whole of the charts for UK and Ireland. I guess, if you're buying in the US, you won't have this benefit. There is a down side to the 298c, it only has one NMEA output/input port whereas the 178c has two. The 298c does though have the Garmin Canet interface for sounder interfacing.