The Mk7 / 7.5 GTI (2015–2021) is, for most people, the sweet spot — the EA888 Gen 3 fixed the worst of the earlier faults, the chassis is superb, and they're plentiful.
Mk7 checks:
- Water pump/thermostat — still a plastic module that leaks (EA888 Water Pump Thermostat).
- Wastegate-actuator rattle at light throttle — usually just noise (Turbo Wastegate).
- Carbon — Gen 3 is better, but a high-mileage DI car still benefits from a walnut blast (FSI Carbon Buildup).
- DSG service (DSG Mechatronic Service); VAQ diff service on Performance-Pack cars (Vaq Front Diff).
- Check for a tune — many are chipped; a clean Stage 1 is fine, a hammered one less so (Stage Tuning Explained).
Bottom line: the Mk7 is the reliable modern GTI to buy — service the water pump and DSG and it's cheap to run. See Buying Mk8 GTI.