I just tested with Ancestry DNA recently. Here are some pros and cons.
Pros:
Ancestry DNA members more often than not have detailed family trees in which you can often find out how you are related to them. If you have a decent family tree, they will give you a list of people who share an exact ancestor. It will provide a detailed chart on how you are related to that person.
Cons:
Ancestry DNA has a match list that is hard to navigate in the way that it is very difficult to access the back pages of your list. A lotof your matches are anonymous.