I have been using familytreedna since 2004. They have run several tests for me. They have the largest database and that is important if you are trying to find others that match your results.
Here is the link to the Kenyon Family DNA project. http://www.familytreedna.com/public/Kenyon/http://www.familytreedna.com/public/Kenyon/ The administrator of this project has the largest database of Kenyon descendants. He knows more about Kenyons than anyone else.
As an example, using my Wright DNA test, 9 of us with matching y-chromosome DNA have been tested. 4 of us descend from one immigrant. The other 5 descend from 4 other immigrants. All 5 immigrants at this point are brickwalls in tracing our ancestries back to Ireland. But we all share a recent common ancestor prior to 1700. None of the descendants of any of these 5 immigrants knew about the relationships with the other 4 immigrants. But with each new immigrant found, we can pick-up new clues to help identify the earlier ancestors.
The other important questions to ask, is how do you find others that may have DNA matching yours.
About the tests, as the other responder commented, the y-DNA test tests your patrilineal line: son to father to grandfather, ... The y-chromosome DNA is passed from father to son unchanged except for occasional mutations.
The mitochondrial DNA does the same from your matrilineal line. This DNA is passed from mother to child unchanged except for occasional mutations.
There is also an autosomal DNA test. This will find cousins with a common ancestral up to find 5 generations back.
I would start with the yDNA test. It has solved several problems in my 40+ years of genealogical research including cracking a brickwall on the parents of my ggg-gf born in 1768. He was either illegitimate or adopted. Those are tough nuts to crack. I tracked down a third cousin to be tested and spent 5 years looking for a match among neighbor surnames. When I found a match, I had a third person tested to confirm that match.
There are more exotic tests, that try to push the envelope back 1,000+ years. I have had one of these, but the answers are more speculative that helpful at this point.
Bill Wright descendant of both James and John Kenyon