there are so many pickups EMG, Duncan, DiMarzio, etc and i want to know what the differences are between them.

Wow... that's a very vague question...

...can you narrow it down a bit?

Well ive used a few, Ive tried the S Duncans, They are pretty good pickups.... Very heavy.

I also have used a B.C Rich BDSM Pickup... That is ideal for thrash... Has that chainsaw sound.

I am still yet to use EMG's but hopefully soon!!

Also used the stock Jackson pickups that come with the Kelly and the India Dinky... Vey metal sounding...

Also tried some other pickups that i dont actually know what brand or make they are.... I picked up the guitar from a "Trade in" Store... It was brand new tho.... Similar to the Rhoads style....

And all of those pickups ^ Were humbuckers...

Ive also tried on my 1st guitar Single coil pickups... I will try and double check the brand for you... But it was on an SX guitar.... They were probably the worst pickups ive tried and they arnt that bad....

All of these pickups were played through a Marshall Mg 100watt fx head and cab... Hopefully soon ill be able to do a Demo video of pickups and show you the different sounds (Y)

Hope i helped... And i know that the information isnt as good as naming all the numbers and names 100% correctly... Ill try and find out properly for you tho.... But my favourite are between Jackson's stock humbuckers.... and the B.C Rich BDSM Passive pickups \m/

http://www.youtube.com/watch?v=j40hklIKHb4 well theres emgs 81+81 on a kv2 (prolly no help bad quality and recording)
i personaly like the "soulless" emgs for the ease of playing just touch the string and it plays
but i think thats just cause the active pick up thigy
go guitar store pick amp and test guitars whit emg s duncans etc if avaible cause trust ur ears cause pick ups are pretty much some like some dont thing

_________________
jackson emg and engl brytality in bound
the power to even destroy theyre very souls.... thus i use emg tehe :3

I'm studying to be an electrical engineer, so I know a few things about this.

Between the brands? I don't really know-- DiMarzio's marketing stresses clarity, SD's marketing stresses warmth, and EMG's marketing stresses gain.

But, in the end, they all boil down to a couple of basic components.

1) A magnet (or magnets, in the case of a single-coil). These are made out of either an alloy or Aluminum-Nickle-Cobalt (aka "AlNiCo") or an iron-dense ceramic.

2) A bobbin made out of plastic or particle board

3) Copper wire

4) Steel pole pieces (in the case of humbuckers)

Ceramic magnets are stronger than almost any AlNiCo magnet, creating a stronger magnetic field, which means that the vibration of the string induces more current, which means stronger electric output.

More copper wire also enhances the magnetic field, but also acts as a resistor, which can limit the treble. If a pickup has more windings of copper wire, it will have a greater output, but will lose some presence.

Really, a decent set of pickups is equal parts science and alchemy-- certain things just seem to "work" for not-immediately-apparent reasons. Your best bet is simply to try out as many as you can (just make sure you are using similar strings, as they can have almost as much effect on overall tone).

Personally, the guitarist in my thrash band just got a set of TV Jones Filtertron-style pickups in his new axe, and they sound amazing through his Mesa Dual-Recto. When you have an amplifier with 6 cascading gain stages, high-output humbuckers, like DiMarzio Super Distortion and Seymour Duncan Invaders, not to mention most of EMG's lineup, become pretty redundant.