Fastest in what sense? Access time? Transfer rate?
For access times, the raptor still rules among consumer hard drives. You need to go to a 15Krpm SAS drive to beat it - or to a Solid State Disk (SSD).
For transfer rates, the very general rule is that the bigger the capacity and the fewer the platters, the faster the transfer rate. RAID-0 can also be used to improve transfer rates (at the expense of extra complexity, cost, and poorer reliability).