I will give this a shot. here is my humble opinion

Garmin, has the easiest menus, have good to fair screen resolutin, they have propietary charting software (bluechart) price wise their software is the cheapest. The also offer a model that includes chart software for the entire U.S. the 192C and 198c I believe

Lowrance has the best by far screen resolution in the mid-size units, 480x480 the 337 is a very nice machine. they also have the most detailed base map, (built in chart) if you don't want to spring for the chart chip. the Navionics chip for lowrance is 199.99 at west marine compared to 140.00 or so for garmin. *The 337 is a high resolution mid size chart plotter that compares in price to their competitions chart plotters but also includes a fish finder that you dont have to hook up, but it is there for the future if you need it. *The menus in the lowrance are a little less user friendly than the garmin but it is not noticible if you have never used a chart plotter and have no pre-learned *habits

Raymarine is probably the cadilac of the machins, the c70, c80 and c120 are great machines with the most versitle opotions, if you only want chart plotter all you will need to buy extra is the Raystar GPS reciever. these units have the most potentioal for expansion but are by far the most expensive, if you never plan to expand, I would not consider them just based on price.

navman has yet to prove itself and their sales reflect that

Horizon Standard make the very best VHF radios that can be purchased, I would never consider another brand, BUT their chart plotters are miserable to use, very awkward menus

Furuno is about the same, they are still running on 5 yr old (approx) software and have miserable menus to try to get around in, crappy screen resolution and are just no fun

I also would not consider buying one on Ebay, I love Ebay and by a lot on there but this is a high dollar purchase and you will want someone close by to provide customer service if you need it. Best way to get one IMHO is to shop the internet, find the very very very best price possible(excluding ebay) on the unit you want print the web page, take it to west marine and they will price match it, then you have the best of both worlds, internet pricing and west marines unconditional satisfation policy Good Luck