We went on several tours with Turansa during our stay in Guatemala. The service was great on all of them and we were taken care of by very helpful and friendly staff.
If you go on the trip to Tikal make sure you stay in the Jungle Inn - For us it was one of the most memorable experiences of the entire trip.
I booked a tour from Guatemala City to Semuc Champey and back. I was very disappointed when they picked me up, to see the bus was full, therefore I had to sit in a fold out chair, and hold my head up and crunch my legs for the next 8 hours on the way to Lanquin. My itinerary did not have the information I required, I kept having to call Turansa to see at what time I would be picked up, and who would be picking me up. On my return, the bus driver that was picking me up was late, so he sent "his friend" to come pick me up... I learned that Turansa does not have their own transportation, they use someone else to transport you and they will not care about your safety, schedule or comfort. Most of all, i was very disappointed to learn I paid almost twice as much as everyone else that went.