Willsboro is the nicest marina on the New York side of the lake with regards to upkeep, facilities, docks, etc. It's where we decided to keep our boat, and it caters primarily to sailboats.
Westport is the next nicest, but the bathrooms and docks aren't quite as nice, parking is restricted, and as you mention - it's on a smaller part of the lake. The wind is usually a lot lower at Westport than up by Willsboro (see http://www.erh.noaa.gov/btv/html/colreef.html
for northern part of the lake and http://www.erh.noaa.gov/btv/html/diamond.html
for near Westport).
Essex is a decent location, but both marinas there have a few issues. I forget what they call themselves exactly, but there are two right next to each other (they used to be one). They both have fixed docks. From what I hear, the southern one doesn't open until June due to high water (docks are submerged). It can sometimes be even later. The northern one opens in May as long as the water level is below 99'. Both have difficult (for sailboats) to navigate configurations.
Price wise, Willsboro is the most expensive, followed by Westport and then Essex. We used to sail out of Westport, and while we like the marina, the location doesn't open up a lot of possibilities for destinations. Out of Willsboro, it's fairly easy to go to Burlington, Valcour, Plattsburgh, etc.
Where are you driving from?