I really like their Android and web clients. I don't use a lot of advanced features, but find it to be very responsive and handles everything I do very well.

I really like their Android and web clients. I don't use a lot of advanced features, but find it to be very responsive and handles everything I do very well. Prior to switching to Fastmail, I used to have my mail forwarded to Gmail but much prefer Fastmail's clients to Gmail now, which surprised me.