For what it's worth, I got my levels up from 7* to 41 using Dr. Best. I don't know if they are the best quality, but it seems to work for me. I take 2 softgel capsules containing 2000IU (so 4000 in total) a day, and have no intention of stopping them for the foreseeable future. My aim is to arrive at 60. At that point I plan to go in maintenance mode.

* I didn't feel too well back then...