Full-frame
A strong option for low light, wide-angle work and shallow depth of field. Bodies and especially fast lenses can be larger and more expensive.
APS-C
An excellent middle ground for travel, family, sport and wildlife. You get strong image quality, useful extra reach and access to compact lenses.
Micro Four Thirds
A compact system with long effective reach and excellent stabilization options. It is especially compelling for travel, nature and handheld video.
Medium format
A much larger sensor can deliver exceptional detail and tonal transitions. The price, file size, lens range and autofocus performance make it a specialist choice rather than a universal upgrade.
One-inch and compact sensors
Smaller sensors can sit behind useful built-in zoom lenses and fit into genuinely portable bodies. They are strong travel and daylight tools when simplicity matters more than shallow depth of field.
Action-camera sensors
Tiny rugged cameras prioritize stabilization, field of view and durability. Their photographs look different from larger-sensor cameras, but they can go places that a conventional camera cannot.
Think in complete lens systems
Before choosing a mount, list two lenses: the one you need now and the one you may add next. Check price, weight and availability. Switching systems later usually costs more than choosing a slightly less impressive body today.