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)
23andMe has declared bankruptcy and has been repurchased by it's founder. The company says all is well and test results are secure. But, do your own research.