As morph says, but add to the fact that SATA2 hasn't got a solid definition.
Sata 2.5, however has, but, at the moment you won't notice any difference.
If you want speed - SCSI is fastest, noisiest, longest lasting.
If you want absolute less hassle, stick with IDE for now. - A lot less problem when tshooting, and, should the system go tits up, unless you have sata-IDE adaptors, they arent as 'universal'.