The best form of vit. D to take orally is D3 or cholecalciferol. D2 is no good, and can be toxic.
Also, from what I know, in order to get Vit. D from the sun, you have to be in the mid-day sun, to get enough UVB rays to make Vit. D (UVA rays do not make Vit. D, & are most damaging to skin...