Second time in Siem Reap and did a car tour for three days the first time, was looking for something different so I found Grasshopper Adventures.
The car tour guide seemed to be able to speak more to the details of the history of the temples but Grasshopper tour guides did not by any means make me feel they weren't also extremely knowledgeable, just probably a different crowd that would participate in different tours.
Overall a great experience. The guide was great, knowledgeable, and was proud to show us and tell us his personal history and the history of Cambodia during the tour.
Only area of critique is the bikes, though in excellent condition and ride extremely well in the terrain, seemed to be designed a little bit differently than what I'm used to where the handlebars seem to be much further away. Partially my fault for not noticing until starting to get fatigued, but after about the third hour it really does a doozy on your back.
They do an excellent job doing their due diligence by asking you your height beforehand so they can prepare for your arrival, but I did another Grasshopper Adventure tour two days later in Saigon (Ho Chi Minh City) to the Cu Chi Tunnels and they had different bikes than the ones Siem Reap did that fitted much better for me. No criticism in how Grasshopper Siem Reap handles their bikes, but just be aware when you test ride their bikes!
Would definitely recommend!