I'd currently recommend BUG, Mrs. Farnsworth, Sarah Jones' Bridge and Tunnel and CVR. Coming soon, all of the major not-for-profits will be launching their seasons, so there are several very promising prodcutions opening in the next few weeks:
-- Paula Vogel's The Oldest Profession (Signature)
-- Basil Twist's Symphonie Fantastique (Dodger Stages)
-- People Be Heard (Playwrights)
-- String of Pearls (Primary Stages)
-- Edward Hall's Rose Rage (The Duke)
-- White Chocolate (Culture Project at the Century)
-- Peter Dinklage in Richard III (The Public)
-- Last Easter (by the writer of "Frozen" -- MCC at the Lortel)
That's just some of what's coming in the next few weeks, not including the 120 offerings of the Fringe Festival, many of which also look very promising.
As for "all-time favorite" off-Broadway plays, I won't even try. I've seen several hundred plays off-Broadway in the last 30+ years and the fact is the vast majority of the finest theatre I've ever seen has been Off-Broadway, not On (and most of the best plays I've seen On Broadway, started out Off-Broadway and then transferred). To try and come up with a list would be impossible (and ridiculously time-consuming) -- suffice to say that The Public, MCC, MTC, the Vineyard, Playwrights, Atlantic, NYTW, CSC, Second Stage, Signature, Primary Stages, and the off-Broadway commercial houses are the heart (and the brain) of the American Theatre.
"What a story........ everything but the bloodhounds snappin' at her rear end." -- Birdie
[http://margochanning.broadwayworld.com/]
"The Devil Be Hittin' Me" -- Whitney