It depends in the design. A well designed round-a-bout is great - a poorly designed one creates problems. A good round-a-bout is NOT a traffic circle. A good round-a-bout forces cars to slow (almost stop) as it enters the circle. There is only one circle lane. It is large enough around so that cars must travel in the circle.

A traffic circle can have multiple lanes which can create conflict with cars in the circle - some want to exit right and others want to continue in the circle. A "button" round-a-bout is a small cirlce. Probably okay for a quiet neighborhood street but not good for a busy intersection. Cars in a button round-about do not have slow to enter the circle and they can go almost straight through which defeats the purpose.

Finally, officials need to better help people know how to go through a round-about. Yield to cars in the circle before entering.