Expect a full or nearly-full train if you decide to travel during the holiday periods. The Coast Starlight and the Southwest Chief will somewhat be full, but since both of them run daily, you have some flexibility in case that the train on your desired date is sold out. As for Sunset Limited, you won't have much flexibility in case the train on a particular day is sold out, since it runs only three times a week. If you are going to Flagstaff or Maricopa, are you wanting to go to Phoenix? If that's so, you can catch the Greyhound from Flagstaff. In case you want to get to Phoenix via Sunset Limited, you are better off getting off at Tucson instead of Maricopa, as the former has the Greyhound stop nearby, and as for the latter, you would have to drive your way into Downtown Phoenix (The Sunset Limited served Downtown Phoenix, Tempe, and Coolidge until 1996, and it is very unlikely that the Sunset Limited will return to Phoenix).