Digital SLRs

For general and travel photography a good compact camera can produce excellent results. But for specialist portrait, landscape, sports and action photography, a digital SLR (DSLR) is worth considering.

Pros
The lens on a DSLR is interchangeable, and the camera may be sold with or without a lens. This means you can change the lens on the camera for shooting in different situations, such as wide-angle interior shots and sports photography.

DSLRs auto-focus significantly faster than compact cameras making them superior for shooting fast moving scenes such as kids' sports. Compacts normally reach 400 or 800 ISO speed, but most DSLRs will achieve 3200 ISO and beyond. This is a big advantage for shooting sports, action and in low-light conditions.

DSLRs have much larger sensors than compacts which affects their depth of field, meaning it's significantly easier to isolate the subject and defocus the background. This makes a huge difference for portrait photography.

Cons
DSLRs are bigger and heavier than compact digitals. Add a selection of lenses and other accessories and they become even less user-friendly for travel. 

Most cameras come with one lens and if you want a new lens at a different focal length you can expect to spend between $350 and $2000. The first new lens for many people is a 55-200mm lens for shooting sports which costs about $380. Many DSLRs can be purchased as a 'twin-lens kit' which includes this lens at a discount.

Micro system cameras

Cameras based on this new interchangeable lens system don’t have the physical mirrors of DSLRs. They’re less bulky than DSLRs and have comparable image quality (in some models) and processing speeds. They lack optical viewfinders, though many have LCD viewfinders instead. 

Most have smaller sensors than DSLRs which means low-light performance isn't as good.