We used Tierra Tours twice in December.
We had a fantastic tour of Volcan Maderas, Massaya market, Laguna D'Appoyo and the Valentine Lopez pottery school; our guide was incredibly well informed and engaging. The tour was very well priced and the vehicle was great.
Then we hired a private driver from the coast to Managua which was priced well for four people, however, to our horror the driver kept nodding off which made for a hair raising nail biting adventure. I asked the driver so many questions about Nicaragua to keep him awake so he finally gave me a tourist pamphlet so I would stop talking. Ironically this entailed him taking his hands off of the wheel to show me the map. I would go with Tierra Tours again...but I would avoid traveling during the siesta hours.