I flew last year on the 763 in BE and absolutely hated it. Cant't sleep on my back and it's tough to try to sleep on your side on this type of seats.
Then I'd rather fly Y and stay awake. The reason why I booked this specific flight were the lie flat seats.
You know, the A333 angled seats aren't bad at all... Some people say that if you're taller than 6ft, it's actually more comfortable since the 764 seats can make you feel cramped.
I never had trouble sleeping on the A333.