What soldering iron do professionals use?

The Hakko FX888D is the station most professional electronics technicians and repair benches in the UK and US train on, largely because of its reliability track record and huge tip/parts ecosystem. JBC cartridge-tip stations are common in higher-end professional and production environments for their fast heat-up and precision. For mobile-phone-level micro-soldering, JBC-compatible C245 tip systems (like the YIHUA 982-V) are widely used for the same fast heat-up reasons at a lower entry price.