often in Handmaid's Tale they comment that this is the most difficult generation. Why is this so?

This is a dystopia. The inherent commonality of these worlds is the paranoia and fear of another ideology threatening the governing party. There is always the imperative to stamp out resistance. Everybody must also sacrifice for the good of the people; their generation is the most difficult. The sacrifices demanded are often horrific. In "Handmaid's Tale" women's' bodies have become the property of the state. In Orwell's 1984, people's identities and personalities are systematically eradicated. The Proles live in poverty and the outer Party exist in a continuous colourless state of sacrifice. In Huxley's "Brave New World" people must live meaningless lives lest the old ways of love, attachment and caring return.

This is the first generation dealing with this change. They are more resistant to it. But future generations will know no other way of doing things. They won't remember pre-gilead ways, thus they won't be tempted to rebel.