The Fusion splits cleanly into winners and losers depending on what's under the hood. The naturally aspirated 2.5L is a quarter-million-mile workhorse that owners genuinely love, and the hybrid drivetrain with its Aisin eCVT is equally bulletproof while delivering 40+ MPG in the city. But the 1.5L and 2.0L EcoBoost engines from 2013 through most of 2019 have a coolant intrusion defect that kills engines between 60k and 100k miles, not a rumor, a documented pattern across dozens of independent owners. Ford fixed it late in 2019, but those earlier turbo models are landmines unless the engine's already been replaced. If you're shopping used, check the engine code before you check the CarFax. Buy the 2.5L or hybrid and you'll understand why some owners hit 250k miles and post about it. Buy a pre-2020 turbo and you're gambling with a motor that has a known expiration date.
The Mazda3 is what happens when a compact car decides it's too good for its price bracket, and the interior actually backs it up. The 2.5L engine is bulletproof (owners routinely see 200k+ miles), but the 2019 redesign swapped the old multilink rear suspension for a cost-cutting torsion beam that blunts the handling sharpness earlier models were loved for. If you want a refined daily driver that feels expensive and runs forever, this works; if you want the sporty Mazda everyone raves about, hunt down a 2014, 2018 instead.