I'd love to hear from anyone who had doubts or regretted the route they chose!
I'm planning on Lima/Cuzco/Machu Picchu trip next year and will likely book with Gadventures. My initial plan was to do the Inca Trail but after researching I decided the thought of a strenuous hike, possible altitude sickness and camping in a cold tent without access to decent plumbing was really not my style. I finally decided that when i'm ready to book I would skip the hike and choose the tour with the train option.
Even though i've made my decision I still feel like I will be missing out on a once in a lifetime experience. On the other hand I don't want to give up the comforts of a warm bed and hot shower in a hotel for sleeping bags and dirty bathrooms on the trail. Will I regret it later? I don't know :-/