I assume by which is best you are referring to which will give you the best interpretation of your ethnic makeup.
If that is what you are looking for the simple answer, in my opinion, is none of them. How these companies "determine" your ethnic makeup is by comparing your results with a panel of "typical" compositions. Where this falls down is that these sample populations are very small and even the best companies only have about 25 such groups at most - to cover a world population that is now about 6 1/2 billion. The science of ethnic genealogy is in its very early day and the results these companies give should at best be taken with a large dose of salt.
That said if you want to test you can test with any of the big three as there are Independent companies like gedmatch and prosapiagenetics where you can upload your results and get alternative analyses. When you see how much some of these alternatives differ you will realise how unreliable the analyses given actually are.
Hope that has not put you off too much. Its OK if you want to do it for amusement but the results are not definitive and companies often claim accuracy that is just not true. If you search previous posts you will find where people have given links where people have given critiques of "ethnic genealogy" testing
