I usually use MP miles to upgrade to F, and I have found that the FAs in F are almost always entirely cordial and friendly, and they give me a pleasant flying experience. Sometimes after using the lav, I engage in a bit of chitchat with the FA in the galley if she isn't preoccupied with duties, and have essentially always enjoyed a fun conversation, albeit brief.

In Y there is less interaction with the FAs, but what interaction there is has been professional and friendly, in my experience.