A number of reputable companies offer DNA tests for genealogical purposes. As a general rule, I recommend that anyone new to genetic genealogy test with AncestryDNA first. They have the largest database of DNA kits by far (see below) and also offer the most user-friendly tools for integrating DNA results with traditional genealogy.
After you get your AncestryDNA results, you can upload your DNA data file to some of the smaller databases for free and get full access to the DNA tools at those sites for a nominal fee. For that, I particularly recommend MyHeritage. They have the third largest database overall and the most robust database for non-English-speaking countries in Europe. MyHeritage also has good tools to integrated DNA results with traditional genealogy. (Note that MyHeritage often has very competitive prices for their own DNA tests, but you’re better off in the long run to upload your AncestryDNA file.)
For additional DNA matches, test with 23andMe. Their “Ancestry Service” test is fine for genealogical purposes, and health reports are available at additional cost.
You can also upload your AncestryDNA results to some smaller databases, including FamilyTreeDNA and GEDmatch. Note that both companies sell access to law enforcement and have a troubling history of violating their own Terms of Service.
Based on my experience working with hundreds of people from different backgrounds, AncestryDNA and 23andMe have the most accurate ethnicity estimates.
Autosomal Testing Growth
Feel free to use the graph above in presentations to genealogy societies and DNA interest groups as long as you cite this webpage as your source. The chart only includes databases that offer relative matching and for which database size is available.