It's all dependant on how you want to sound. All I can do is give you suggestions and tell you how much it might cost to put in. The pickup you want is dependant on how you want to sound. So there are a few things to consider before getting a new pickup. Do you play heavy, hard, slow, fast, light, quiet, loud, etc.
Most pickups have a certain volume they operate best at.
Some pickups have more high end than others. I wouldn't recommend coming on the Nirvana board and asking what pickups you should get. In fact, you may hate it. Most pickups have a certain peak in the frequencies, meaning they'll either have too much bass, too much midrange, or too much treble for you. Some pickups have a certian way they feedback and distort.