A long time ago, in a past life, I used to work as a lab tech at Memorial Sloan Kettering Cancer Center (68th Street and 1st Avenue) passing cells and running gels as they say in the molecular biology business, LOL.

I commuted in from Brooklyn Heights and it was not hard (to me anyway). I cross the Brooklyn Bridge, ride uptown along Centre Street then Lafayette Street until it hits Astor Place, then hop east one block to 3rd Avenue, which I take all the way up to 68th Street.

This is down-and-dirty street-riding though in Manhattan motor traffic, and requires the utmost caution. Did that for 4 years and I survived.

I also tried the East River bike path just once, and frankly it's an unnecessary detour that adds a couple miles to the commute (because it makes a huge superfluous loop to the east) so I never bothered with that.