The seat comfort in C and F on Emirates is often critizized here at FT. For day time flights the seats are perfectly fine, and i have slept perfectly fine also on the longer routes, however the seat comfort can not be compared with that of carriers such as BA that offer lie flat seatings.
I have had 10 EK C and F flights this last year however mostly 4-7 hour flights, so my opinion is based on this...