Gossen Multisix (hand-held, incident and reflected light meter) whenever I can bring it with me, which is quite often.
Minolta Spotmeter if it's complex work such as nocturne photography with slide film, slow tripod work.
In-built light meter for casual photography (e.g. during hiking with my Yashica T3), of photography with a general purpose zoom (real f/stop not necessarily accurate, so an external light meter requires a little bit of caution).
Generally speaking the in-built light meter is the residual choice. Slide film here so exposure is quite important to me.