Jerry rice had a great work ethic, but I've seen plenty of "better" receivers than him.
Paul Warfield, Lance Alworth (I liked Otis Taylor too) and more were better receivers but didn't have the work ethic and consistency year after year and didn't play as long.
Rice has earned every accolade he's received but, he's more a Hank Aaron than a Willie Mays. Aaron maintained a high standard for years and piled up the numbers, but no one thought he was better than his contemporary Mays as a baseball player.
I'll go out on a limb and say Randy Moss is the greatest receiver I've ever seen. I wasn't happy with his attitude or incidents prior to this year, but was always amazed with his athleticism.
Having watched football since 1960-61 or so, I can say I have not seen a receiver that can do what he does, not even very close.
He's smooth, he's fast and the adjustments he makes to catch balls are pretty much ridiculous.