We used Wildebeest Safaris LTD for Kenya and Tanzania in June 2015 and had an excellent experience with them. OlyEsteban is correct, the guides all seem to know each other and communicate via CB or cell phone, so you should see a lot more animals if you use a guide. For our trip we had private guides, which isn't much more money than the group trips, but we always had the best view and could choose whether to stay longer at a particular place or move on. Noah at Wildebeest Safaris was very good at creating a custom trip based on what where we wanted to go.