For room interiors, an ultra-wide lens is usually the practical choice, but going too wide can make the room look distorted. A good rule of thumb from the examples given is around 10mm on APS-C, or roughly 16mm on full frame, which is often wide enough for small rooms while keeping lines more natural.

If budget allows, a full-frame camera with a wide zoom such as 16–35mm gives strong image quality and flexibility. A very wide prime like 14mm can work too, but the wider you go, the more exaggerated the perspective can look.

A more affordable option is an APS-C camera with something like a 10–22mm lens. That gives a useful wide field of view for interiors at lower cost.

Another good approach is to avoid using the widest setting all the time and instead shoot multiple overlapping frames, then stitch them into a panorama. This can make rooms look more natural than a single extreme wide-angle shot. A panorama head that rotates around the lens’s optical center can help stitching accuracy, and software such as AutoStitch was suggested.

So: for simplicity, choose a wide zoom; for the most natural-looking results, consider panorama stitching.