Short answer: Add your expected premiums to your likely out-of-pocket costs (deductible, copays, and coinsurance up to the out-of-pocket maximum), then factor in any HSA or employer contributions. The lowest-premium plan is not always the cheapest overall.
A plan’s premium is only part of the picture. To estimate your real annual cost, add up your yearly premium and your expected out-of-pocket spending for the care you actually use. Your out-of-pocket exposure is bounded by the plan’s out-of-pocket maximum, which is the most you would pay in a year for covered in-network care before the plan pays 100%.
Think through your expected usage: routine visits, prescriptions, and any planned procedures. A high-deductible plan with a low premium can be cheaper if you rarely use care, while a higher-premium plan can be cheaper if you expect significant medical costs. Account for money that offsets your costs too, such as employer or self-funded HSA contributions, FSA dollars, and any premium tax credits on the marketplace.
A useful comparison is: annual premium, plus likely out-of-pocket costs, minus employer or tax-credit contributions. Running that math for each plan option, including a low-use and a high-use scenario, usually reveals the best value better than premium alone.