Whether you're buying headphones for yourself or for a child, it's important to consider the design — but that shouldn't be the only consideration.
Size and durability
There are several different types of headphones — each with different audio attributes and designs. If you're looking for a pair to use while commuting, consider whether they'll be stored inside a backpack, around the neck or in a pocket, as this will determine the maximum size of the headphones. Durability is also a major factor in choosing headphones.
Ear-bud earphones are usually the cheapest style of headphones available. Constructed from plastic and sitting in the outer ear canal, they are easy to insert and remove. Their small size allows them to be stored in a pocket, wrapped around an MP3 player.
In-ear earphones or 'canalphones' are a similar size to regular ear-buds, but they sit in the inner ear canal. This provides some acoustic noise cancelling — blocking outside noise, allowing lower earphone volume levels — but in-ear earphones are harder to insert and remove. They are also generally fragile and can be broken unless carried in a case.
On-ear headphones are larger than ear-buds but generally smaller than full-size over-ear headphones. They are harder to carry around when not in use due to their larger size and greater weight, but 'portable' models may fit into a jeans pocket at a pinch. The cables of on-ear headphones are often their weakest point, but the headphones are usually sturdy.
Full-size headphones, colloquially known as 'cans', are available in both 'open' and 'closed' varieties, with the latter blocking out some outside noise due to a tight fit. They are generally bulky and do not fold for travelling, making them a poor choice for anyone constantly on the move. On the flip-side, they are generally well constructed and durable.
Closed vs. open design
After choosing your headphone style, this is the next major decision to make. Closed headphones have a tight seal, either around your ear or against your ear canal, to block out ambient noise. More expensive full-size headphones may also have 'active' noise cancelling which uses microphones to detect outside noise and circuitry to cancel it. Closed headphones are often criticised for delivering less detailed audio than their open counterparts — you will have to weigh this up against the advantage of reducing ambient noise.
All in-ear earphones have a closed design, and all ear-bud and on-ear headphones are open. If possible, try the headphones for a short while with a portable music player before buying them.
If sound quality is a concern, purchasing full-size headphones will ensure the best possible sound quality. In-ear earphones will also almost always have better sound quality than their ear-bud headphones. In general, the more you spend the more accurately your headphones will reproduce music — though there are several stand-out products that offer good sound for a low price.
Wired vs. wireless
Some headphones are available with Bluetooth wireless connectivity, allowing them to directly connect to compatible MP3 players and mobile phones without any tangle-prone cables. Wireless headphones' sound quality is generally poorer than wired models but the added convenience is a huge bonus.
A pair of headphones can cost as little as $5 or as much as $5000. While your initial instinct may be to buy the cheapest pair you can find, investing in a more expensive pair may mean they last longer, sound better and fit well. If you're interested in music or are undertaking a music-related course such as DJ mixing, you can find headphones tailored to your needs. Above $200 the law of diminishing returns sets in, with minimal increases in sound and build quality for the price you pay.