The fit isn’t always an easy thing to be sure of when you can’t try before buying, since some ear pads will not have a satisfactory fit to some ears. Power requirements aren’t a simple matter of looking at the impedance, since efficiency or sensitivity doesn’t always track directly with impedance. Another issue indirectly related to power requirements are whether the headphone has the option for ‘balanced’ use or some other connection that isn’t a 3.5 mm or 6.35 mm jack and plug.
Earbuds have small speakers that rest on the ear canal of the wearer. These are usually much less expensive than on-ear and over-ear headphones and reproduce the sound well. However, outside sounds, such as traffic or power tools, can get past the earbuds and interfere with your enjoyment. Earbuds also don't stay in place very well if the wearer is moving much, such as exercising. These also are lower fidelity than on-ear and over-ear headphones.