What is a good ssri to take for anxiety problems and please explain why?

Any SSRI can be good. If it work for you, then it is good. The reason why is that they are all ssri, and therefore all can work for anxiety. On the other hand, for unknown reasons, some individuals do better with some, and not with others. This may be especially relevant when it comes to side effects. More likely individuals differ on side effect than on efficacy. Also, ssri is not the only class of drug to consider.