Can you tell me which one of those uses Quest? I used Life Extension as well for vitamin D but had to go pretty far to get to a LabCorp facility. I've got a Quest facility a few minutes away I'd rather go to.
Choice of Quest or DirectLabs: Walk-in Lab (switch the radio button to Quest on the category pages, and make sure a "QD" icon shows up next to it in your cart), TrueHealthLabs (make sure the tests you look at say Quest is an option), HealthTestsDirect (make sure the test list page is toggled to Quest at the top)
DirectLabs and Walk-in are generally cheaper than the others I mentioned.
Quest-only: DirectLabs, Personalabs
Choice of Quest or DirectLabs: Walk-in Lab (switch the radio button to Quest on the category pages, and make sure a "QD" icon shows up next to it in your cart), TrueHealthLabs (make sure the tests you look at say Quest is an option), HealthTestsDirect (make sure the test list page is toggled to Quest at the top)
DirectLabs and Walk-in are generally cheaper than the others I mentioned.