Short answer: An HDHP has a lower premium and lets you fund an HSA, but a higher deductible before coverage kicks in. A copay plan costs more per month but gives predictable, low point-of-care costs. The best fit depends on expected usage and cash flow.
High-deductible health plans (HDHPs) and copay plans solve different problems. An HDHP offers lower premiums and HSA eligibility (a triple tax advantage), but you pay more out of pocket before most coverage applies; good for healthier people or those who can fund an HSA. A copay plan has higher premiums but predictable, low costs at the point of care; good for people who use care often. Compare your expected annual usage against the premium difference, remembering the out-of-pocket maximum caps your worst case either way.