JCL is right, you have to decide what is most important to you. There is a trade-off for everything. From what I have heard, slotted rotors will give you better stops in wet conditions, but will eat up your pads faster. I am considering using StopTech direct replacement slotted rotors (same size as OEM, just slotted) and Axxis Metal Masters when I replace mine in the near future, but I am willing to deal with a little more dust and noise for increased performance. I have that exact combo on my 325i and have been happy with it.

I think there have been many post about this topic. If you do a search for "brake rotors and pads" you may find additional info. If all else fails, you can never go wrong with original equipment.