I cannot be exposed to sun or light for that matter so I have to supplement with Vitamin D. I like NOW brand liquid D3, I take it daily and my levels are now in the normal range. I think D3 tablets are sub-optimal for absorption reasons, also many contain fillers which can be harmful
I live in south Florida, got plenty of sun, and took a high level organic, vegan Vitamin D supplement. My levels were still way too low. I was not absorbing it correctly (in addition to a variety of other vitamins that my body was not processing). I currently take 2000 IU's a day through a liquid supplement that my holistic nutritionist ordered for me. It is very important to check your levels through blood testing. Too low can lead to many illnesses.
I also agree with Laurie, you want to make sure, as with any supplements, that you take a good quality one. Most supplements out there are full of fillers and have no where near the levels of vitamins that they purport to have in them.