This is very much dictated by price and brand. If you’re looking for in-ears for sports, look for models with ear clips that will better anchor the buds to your head. Water resistance is well worth having too. More expensive earphones will often pack more processing power, and boast algorithms that elevate lower quality streams to something approaching hi-res audio.
Noise cancelling is perhaps the ultimate feature differentiator. Very low cost in-ears will probably not offer noise cancelling, but step up the price ladder and you’ll find some models with excellent Active Noise Cancelling.
When you’re going wireless, also consider which version of Bluetooth is being used. The latest versions, we’re now on 5.0, are more battery-friendly. AptX Bluetooth indicates that sound quality has been prioritised. It can transmit music at 16-bit/44.1kHz, often described as CD-like.
Aptx Bluetooth HD is a significant step up the performance ladder. Developed by Qualcomm, this Bluetooth codec is able to transmit 24-bit hi-res audio, between compatible hardware.
Some brands, for whatever reason, snub aptX HD in favour of a rival technology, known as LDAC. Invented by Sony, it has been adopted by various makers. LDAC allows high-res audio streaming over Bluetooth, up to 990 kbps at 24 bit/96 kHz.
The most recent wrinkle in the codec story is aptX Adaptive. It’s a mix of aptX HD and aptX Low Latency, the latter having been developed for gaming applications and video playback with improved syncing (said to be less than 40 milliseconds).