Personally, I don't feel like there is a wide variety of playability in the class 1's for horn. But I have found Nocturno (op.7) by Franz Strauss to be playable for some of my average players. Check the list to make sure it is still a 1.
But I do have to agree with some of the others on here: If they aren't a strong enough player, then they need to play a class 2 if they are still able to. There are plenty of 2's that are challenging.