Haven't seen Living Together yet, but if you are only seeing one... between Table Manners and Round and Round the Garden, I'd personally recommend The Garden.
I felt it was a bit more "complete" as a stand alone with more sense of closure in the end.
Living Together, after just reading it, has a much clearer balance between comedy and drama, though Table Manners has much more, and occasionally better comedy, but the ending of Living will leave you so shocked, it's almost a better choice to see Living Together
Living Together, after just reading it, has a much clearer balance between comedy and drama, though Table Manners has much more, and occasionally better comedy, but the ending of Living will leave you so shocked, it's almost a better choice to see Living Together