I've seen both. As much as the softest part of my heart wants to say Flying, I think the answer is Clyde's. It's just superior, period. Flying has lots of individual parts that recommend it - great performances by great performers, beautiful sets and design, a uniqueness factor that is pretty much unmatched. But the whole is much less than the sum of its parts. Clyde's however, is tight, funny, smart, extremely well acted and it's not just a throwaway comedy, it's very moving and carries more weight than may seem at first glance. Plus I think it will one day be an impressive dinner party talking point to have seen Kara Young at this stage of her career, I think she's going to be major.
I'm a musical lover, obsessed with Carmen Cusack and aware of the importance of Lapine - and I would recommend Clyde's.