The recent database numbers for the major DNA companies are as follows:
23andMe 14,000,000
Family Tree DNA 1,661,040
Ancestry DNA 25,000,000
MyHeritage 8,500,000
Living DNA 300,000
Chosing a company still requires an answer to the question: "Where would my relatives be most likely have taken a DNA test?"
23andMe and Ancestry will NOT take uploads from other companies. The rest will (there may be a small fee to use the full set of tools at the site)