Start by choosing a system, not just a body. Your biggest long-term investment is usually lenses, and those will matter more over time than the first DSLR body, which will age faster technologically.

A good approach is:

• Don’t overspend on your first body.
• Plan significant budget for lenses as well; roughly splitting your initial budget between body and first lens is a reasonable starting point.
• Handle cameras in person and choose the one whose controls, menus, and ergonomics feel natural. Comfort matters because it affects how quickly you can react.

For your subjects:

• Action/indoor shooting benefits from good high-ISO performance, decent burst/buffer performance, and responsive autofocus.
• Landscapes are less demanding on the body; most DSLRs can do well here.
• Macro/nature often depends heavily on having the right lens, and for wildlife or distant subjects you’ll likely want a longer lens, around 200mm or more.

Many buyers narrow the field to major systems such as Canon or Nikon because of their broad lens ecosystems and strong used markets, then choose based on handling and lens availability for the kinds of photography they do.