Background Medicaid expansion and subsidized private plans purchased on the Affordable Care Act’s (ACA) Marketplaces accounted for most of the ACA’s coverage gains. Objective Compare access to care and financial strain between Medicaid and Marketplace plans, and benchmark these against employer-sponsored insurance (ESI) plans. Design Cross-sectional survey Participants A nationally representative, non-institutionalized sample of 37,219 non-elderly adults with incomes up to 400% of the federal poverty level between 2015 and 2018, and a sub-group of individuals with chronic diseases. Main Measures Self-reported barriers to accessing care, cost-related medication non-adherence, and financial strain. Key Results Marketplace enrollees were more likely than Medicaid enrollees to delay or avoid care due to cost (19.3% vs 10.0%; adjusted difference (AD), 8.6 [95% CI, 6.8 to 10.4]) and report difficulties affording specialty care (7.7% vs 6.6%; AD, 1.8% [95% CI, 0.3% to 3.3%]), while there were no differences in having insurance accepted by a doctor or ability to afford dental care. Marketplace enrollees were also more likely to report cost-related medication non-adherence (21.5% vs 20.0%; AD, 4.0 [CI, 1.5 to 6.4]), be very worried about not being able to pay medical costs in case of a serious accident (32.3% vs 25.8%; AD, 6.4 [CI, 4.2 to 8.6]), have expenses exceeding $2000 (22.4% vs 5.4%; AD, 8.3 [CI, 6.2 to 10.3]), and have problems paying medical bills (18.4% vs 15.6%; AD, 1.8 [CI, 0.3 to 3.9]). Marketplace-Medicaid differences were larger among persons with a chronic disease. Individuals in ESI plans fared better for most, but not all, outcomes. Conclusion Medicaid offers better protections than Marketplace plans on most measures of access and financial strain. Supplementary Information The online version contains supplementary material available at 10.1007/s11606-021-07100-0.