A pickup is a device which detects the magnetic field disturbances produced by the vibration of the string and converts it into an electric signal, which is then converted into an audio signal. This is why electric guitar strings are made of nickel.
So in essence, the pickups are the first part of the chain of amplifying your sound. They ‘hear’ what is played, and then send it through your cables to the amp.
The differences in pickups create differences in resulting sound. As such most guitarists have a preference, depending on their preferred tone. Below are the main kinds of pickup, with a bit of information on each one, the type of sound created, and which guitarists favor these pickups.
Single coil pickups are very common, but are often almost synonymous with the Fender Stratocaster, and most strat-copies and strat-type guitars.
Though of course subject to the effects/amps through which they are run, single coils are generally known for brighter, thinner, twangier tones. This means they’re a popular choice in genres like funk, country. However, the ubiquity of the strat means it’s fair to say rock, pop and blues too.
However one downside is that single coil pickups are susceptible to humming and excess noise meaning other pickups are often preferred for heavily distorted, high-gain sounds.
The humbucker is a dual coil design, which generally produces a fatter, warmer tone than a single coil pickup. This, plus the reduced hum (thanks to the addition of a second magnetic coil) means many guitarists prefer humbuckers.
Particularly guitarists who play heavily distorted rock/metal – as humbuckers better handle the high gain, or Jazz, thanks to their warmer tone.
Humbuckers’ higher output means they do clearly win in these genres or others where a high output is required. Evidence of this is clear in the list of famous guitarists who use humbuckers, such as famous Les Paul / SG playing legends Jimmy Page and Slash.
However, they just don’t suit the thinner, twangier sounds required in country, funk, surf, soul, etc and in fact, regardless of genre, some guitarists will always prefer a Strat (single coil) over a Les Paul (humbucker), so don’t forget to factor in your own taste, style and preference!
The P-90, made originally by Gibson, since replicated by others, is an attempted compromise, a tonal blend between single coils and humbuckers. Exactly what’s required by the significant number of guitarists who prefer the single coil sound but the humbucker’s high output and excess-noise-reduction.
The P-90’s tone itself is characterized by being both bright and thick. The bass response is good, despite the clarity of the top end.
So whilst the single coil suits the bright clean sounds of funk, country and soul, and the humbucker suits the heavier high-gain metal/heavy rock genres, the P-90 pickups are really well suited to that middle ground of blues/rock.
As such, they have – at times – been the pickup of choice for guitarists like Dave Gilmour and Pete Townshend.