A lot..... Go to the different manufacturer's website's and do some research. Harmony Central has a section for reviewing pickups if you want to brows what people have to say about certain pickup's, but don't completely go on what you read there. There's no one best pickup manufacturer. Everybody has different taste in tone, so while SD's may work for Billy over here, Johny may prefer DiMarzio's. They all have something different to offer.