Nishiki Sport, Downtube IXNS, 1950's MMB3 Russian Folding Bike, MTB
Advice wise I'd say go counterclockwise. That way you get to walk up some hills and ride down (as opposed to ride up and walk down).
Go up the East side, hit 119 (take the overpass over the FDR - if you miss it you'll see a big pile of sand; just back up a few blocks till you see the sign that says you should have gone across) and ride across to Adam C Powell - take that up to 153rd. Cross the street, go on the sidewalk or against traffic (there's really no other way here) and cross over 155th. Hang a left. Enjoy a really long uphill. At the first traffic light look to your right, the bike path picks up again. At the bottom of the hill you have to cross over and go 'into' the divider where it picks up again. Enjoy a few miles along the water to your right and traffic backed up on the Harlem River Drive on your left
That ends and you're back in traffic. You can either go straight across or hang a right and go a few more blocks to the tippy top. I usually head across.
After a few blocks you'll see a big intersection with a tiny sign to the left, following signs for the Hudson River Parkway. Go that way. You'll go up a hill, then have to cross a nasty entrance, go down a small hill under an overpass and walk up. Now you're on the west side and can pretty much go down the rest of the way to the Southern tip except for a few well marked places to detour.
PM me if you'd like to do it sometime; I'm leading a few friends this upcoming Saturday.
30 some miles around the Island.
Not hilly, can be crowded in many places, isolated in others.
Last May at BNY5B I rode down the west side in the morning and up the east side after the main ride. East side is a rougher ride than the west side. Watch your turns, the route is easy to miss in several places.