Both of these units use different charting software. Look into the software that is available for both Garmin and Raymarine unit so that you can be sure that they cover your desired areas adequately ... AND ... how much the software costs. The Garmin uses Garmin/Bluechart and the Raymarine uses Navionics.
My preference is the C-Map charts. This has to due with both the layout of the C-Map software AND the fact that our big local lake (Winnipesaukee) is only on C-Map and Garmin. Additionally, the cost per coverage is best with the C-Maps. However, each person will have their preferences.
I choose the Northstar 557 unit. This is a 5" display, takes the C-Map cards, has much higher resolution than other units in the price range ($500 to $600) and also has provision for a fuel flow monitor ($80 to $100) so you can monitor your GPH and MPG. And ... now that it's installed ... it works wonderfully!
I purchsed the Northstar 557 and 2 charts (Northeast Lakes and East Coast) for a total of $825 delivered (on ebay).
