I've been here twice and it's always packed! The thing I like about Pai that's different from Sukho Thai and Khao San Road is that they take reservation (unless that has changed recently).
As a party of three, two of us got chicken pad thai with medium spice and my other friend tried their Gaeng Masaman with braised beef. We also shared a thai iced tea which was comparable to authentic thai iced tea you could get in Thailand (according to my friend).
Overall, I thought the food was quite delicious and flavourful.
During my other visit, I tried the Pad Gra Prow which I actually really enjoyed as well. I will definitely be back in the future.