sRGB
The standard colour space of the web, most consumer displays and untagged images, with a relatively small gamut.
In depth
sRGB is small, but it is universal — any browser, phone or lab that receives an untagged file will assume it. That makes it the correct choice for final delivery online, where a wider space would be misinterpreted and render dull and flat. It is a poor choice for editing, because it cannot hold saturated cyans and greens that the camera captured.
Examples in practice
Exporting a file in Adobe RGB to a website that ignores profiles produces visibly desaturated, greyish colour.