Do AirPods have sound delay?
Yes, there is a noticeable delay (latency) with the AirPods. This is so with any wireless headset - but the amount varies according to the chosen codec, quality (frequency range, samples per second, etc), and protocol.

Basically any wireless headset has to balance bandwidth, latency, power usage, etc.

If you use AirPods for streaming music, playing videos, etc. the delay is not a problem. The AirPods will use higher quality settings for the best audio possible.

If you use AirPods for phone calls, Siri, or similar - the quality settings are automatically lowered to better balance these factors for that use case. In some cases you're perfectly okay with 8 kHz mono sound.

If you intend to use AirPods for listening to virtual instruments in GarageBand triggered by a MIDI keyboard - you're not going to enjoy it. These instruments require a high quality setting for the audio to sound their best - but you'll then have a very noticeable delay (latency) between hitting the keyboards on the keyboard and hearing the sound from the AirPods. 

For those types of scenarios, wired headphones are still the best.