There is no single “best” product— the best vitamin D is the one that safely meets your needs. Supplements mainly contain vitamin D2 (ergocalciferol) or D3 (cholecalciferol). Both are well absorbed, and absorption is improved when some fat is present in the gut. D3 is commonly preferred in practice, but the most important factor is correct dosing and consistency. Choose based on your goal (repletion vs. maintenance), medical risks (kidney disease, granulomatous disorders, drug interactions), and adherence (drops vs. capsules). Because vitamin D is fat-soluble, unnecessary high doses may increase risk; higher serum levels are linked with potential adverse effects. The “best” option is a reliable, well-standardized supplement used with appropriate monitoring to reach a suitable 25(OH)D range.