Just wanted to give some feedback on the operator I traveled with in Turmenistan: DN Tours.
I had an amazing tour through Turkmenistan with this company (Uzbek Border Farab-Merv-Mary-Ashgabat-Darvaza-Konya Urgench-Uzbek Border Dashoguz). The manager of the company, Gulnara, is very helpful and responsive and managed everything perfectly. Not only she quoted the cheapest prices, but the options and advice she offered were also the best I had been given (I contacted a dozen companies before making my decision). I got an English-speaking guide and private drivers, as well as free entry at archaeological sites, while other tour companies had quoted a much higher price for tours that did not include any guide (just a local driver who does not speak English). Unlike other tour operators, if you don't want to hire a private car, DN Tours offers you to travel by train (night train from Mary to Ashgabat in my case) or local buses for a cheaper price. You also don't pay anything until the turkmen authorities have issued your LOI (letter of invitation needed to process the visa), and Gulnara kept me updated on whatever information she got during the LOI application process. She always replied to my emails extremely quickly.
Traveling with my guide, Diana (21 years old), felt like traveling with a friend, as I am a woman in my 20s. I had not specifically requested to have a female guide around my age, but I thought it was very sensitive of Gulnara to arrange for her to be my guide, as we definitely had a lot to talk about and it was interesting to get to hear her perspective on Turkmen society. They also have other guides who speak different languages (French, German etc.). Although I usually travel solo and I enjoy being alone, I have to admit that having a guide made things easier, as I would have struggled with the language (Russian and Turkmen only) and I would not have learned as much about the country if I had been alone. I enjoyed learning about Turkmenistan, and Darvaza crater was a stunning experience I'll remember all my life.
The food was also great and the whole trip (train, car) was very comfortable. Tours are tailor-made and they are a great value for money. I would strongly recommend this company to everyone.