There is a third option on many cameras that is worth knowing about because it is often the best default: electronic first curtain.
It starts the exposure electronically and ends it with the mechanical shutter. That removes the vibration from the shutter opening — which is the part that causes shutter shock — while keeping a mechanical closing, which avoids most rolling shutter effects.
The catch is that at very fast shutter speeds with a wide aperture it can produce uneven exposure or oddly shaped out-of-focus highlights, because the electronic start and mechanical finish do not travel identically.
So a reasonable set of defaults:
- Electronic first curtain for most work.
- Full mechanical for very fast speeds with fast lenses, and whenever you use flash.
- Fully electronic for silence, and for static subjects where vibration matters.
- Avoid fully electronic for fast motion and under artificial lighting.