For most people, 30-50 ng/ml is probably good. If you have a specific reason to go higher, the Vitamin D Council has useful information supporting that line of thought. Personally, I find that higher levels, around 60, help me to avoid the common cold.
Chris Masterjohn has written against
the "naked ape" theory (that we evolved to live outside, exposed to lots of sun, getting tons of vitamin D) and has pointed out that traditional diets are much higher in Vitamin A. A lot of the Vitamin D boosters think people get too much Vitamin A. So that's another source of disagreement (Vitamins A and D work together but are also mutually antagonistic.)
Since I get more Vitamin D, I figure it is more important for me to get the various co-factors (like the K2, mentioned above): https://www.vitamindcouncil.org/about-vitamin-d/vitamin-d-and-other-vitamins-and-minerals/
Dr. Cannell, who runs the Vitami D Council, has put his name on a Purity Products "Advanced D" formula, which has 5,000 IU's of vitamin D, with rather small amounts of the different co-factors (it's on Amazon). It is a bit pricey ($30 for a month's supply), but give you an idea of what he recommends for most people (even with the annoying proprietary blend part).