0.25 mm. It is where most people printing figures end up, and the reason is reliability rather than resolution.
Why not 0.2 mm
A 0.2 mm nozzle does resolve marginally finer detail, and it pays for it twice: its flow band is only 1 to 3 mm³/s, and its orifice is small enough that any pigment agglomerate, any dust, any slightly filled filament will block it mid-print.
The nozzle reference on this site describes it as the finest detail available on a consumer machine and by far the slowest — a part that takes two hours at 0.4 mm can take most of a day. For a shelf of figures rather than a single showpiece, that is not a practical trade.
What 0.25 mm actually delivers
A 28 mm figure on a 20 mm square base, at 0.1 mm layers and 50 mm/s, takes 54 minutes and uses 3,215 mm³ of plastic. At 0.05 mm layers it takes 109 minutes.
Its 0.28 mm line width resolves the features a 28 mm figure actually has — belts, straps, facial planes, weapon edges — and its 2 to 4 mm³/s band, while slow, is enough that the print finishes within an evening.
The layer height is doing more work than the nozzle
Nozzle diameter sets how fine a horizontal feature can be. Layer height sets how smooth a curved or sloped surface looks, and on a figure that is most of what you notice.
So 0.25 mm at 0.05 mm layers looks dramatically better than 0.25 mm at 0.15 mm, while 0.2 mm versus 0.25 mm at the same layer height is a difference you have to look for.
What to avoid entirely
Any filled or abrasive filament. Wood-filled, carbon-filled and glow-in-the-dark PLA all contain particles that will jam a fine nozzle, and glow filament is abrasive enough to widen one before it blocks it.
Print figures in plain PLA or a resin-like silk grade, and keep the filled materials for the 0.4 mm nozzle.
Compare the two sizes in the 0.25 mm nozzle reference and the 0.2 mm reference, or model your own figure in the print time estimator.