This trek was fantastic, we went to so many amazing places that you wouldn't get to on your own. Highlights were the national parks, especially Big Bend. The trek was great because it had a great balance between cities and the middle of nowhere (literally). We met so many interesting characters along the way and formed friendships with those on our trek. Our tour guide was fabulous - he had so many tips and tricks up his sleeve that made the trek that little bit better.
As well as this - travelling in Winter is awesome! Even though it was a tad cold in some points (-26ºC, shhh, don't tell anyone!) it was amazing because there were hardly any queues for places, you got to do things you wouldn't be able to do in the summer, and you got a huge variety of weather - snow one day, then a week later basking in the sunshine in the desert. Amazing! Snow at the Grand Canyon, not something everyone gets to see - and even better because you aren't surrounded by other tourists shoving their cameras in your face.
I would seriously recommend this tour for anyone who is thinking about travelling the US!
Tip - definitely do the tour starting in New York and ending in LA (you gain hours across the time zones instead of losing them, and your last night is a great chill out time spent with your friends!)