Hi Mary,
I've been on two of JY's American holidays (National Parks and Hawaii) together with tours to South Africa, China, Jordan and Iceland.
I can recommend all of the tours I've done but the USA National Parks has to be my favourite so far. Stunning scenery, history and the bright lights of Vegas for a night at the end - absolutely brilliant!
JY have made some improvements to the Hawaii trip since I went (most notably to the travel arrangements by flying direct to San Diego on the outbound journey and having 4 nights on Maui instead of 3), so I can recommend that as well.
As Lesley07 has suggested, you might also like to consider the Golden West tour if you're planning to travel in Sept/Oct time. I haven't done this trip myself but if you look in the 'reviews' section I'm sure you'll find some very positive comments from people who have done this trip in the past.
Hope this helps you come to a decision.
Cheers
Mike