Don't mean to sound snarky, but I respond better to 'name your favourite ___s' rather than 'name your x favourite _____s'.
Although I have them all, and multiple recordings of many, they're just so consistently good, and so bloody numerous, that maybe I still don't have any overall favourites, or rather: the ones I could name as my favourites are the ones I spent the most time with--not necessarily because they're my favourites. And yes I know how convoluted that sounds. And sometimes I'm thinking, 'what number was that one with...?'
That said, 51, a solo cantata for soprano, springs to mind.
Saying cantata 191 is cheating, but it does have some of the most beautiful music he ever wrote.