There has been a trend lately (mostly on Trip Advisor) that you should only use taxi drivers that you know, as opposed to just hailing a random red plate on the road. As others have said, if you find a driver that you like and he is available, by all means use him. If you find yourself in a pinch and you don't have arrangements with your personal driver (which happens to me often) you can either ask the folks running the establishment where you are to call you a taxi, or you can walk to the road and hail one. 99.9% of people that hail random taxis (route or otherwise) will tell you that they never had a problem doing so.

We have a private driver that my wife and I love. On our last trip, we gave him a lot of business and by the end of our stay I would ask him how much I owed him for a ride and he would say, "just pay me whatever you want". That's an honest driver.