How accurate is Ancestral DNA Testing?

I have been doing my family genealogy as a hobby for about ten years now. I have hit a brick wall and can go back no further. I'm thinking about doing ancestral DNA testing, and I want to know how accurate it is, if at all and also, what would be the best company to go through for that to get the most accurate results. Thanks.

Does anybody have any ideas of what would be the best company to go through for Ancestral DNA Testing. There are so many, and I don't know which is the most accreditted. I would appreciate any advice. Thanks.

I want to do ancestral dna testing to prove what i found doing my family history. What is the best company to go through, cause I know there are some phonies out there. Any ideas?