Seagates (esp Barracudas) have always been the quietest range of desktop hdds for the last 5 years. WD have better reliability and speed however, which is why theyre more common - seagate is a company that concentrates on their enterprise market (as in scsi hdds, raid arrays, serial attached scsi etc) so they don't promote their stuff as much, and the technology from enterprise eventually trickles down to the consumer level.. that said, Im running the 1tb WD drives for data storage so I'm not really concerned about noise... If I was building a silenced rig (without SSD's) I'd be using the seagate drives in a silenced and cooled enclosure... however SSD are totally silent, very reliable and generate almost no heat - their only downside at this point in time is write speeds and the cost
People are using 2.5's because its no longer necessary to have 3.5" hdds. Back in the old days, a 10mb hdd would take up 2x 5.25" bays, and when the 80386 came out they had 3.5" hdd's (this is circa 91 give or take a year)... from next year onwards you'll be seeing cases with 2.5" hdd bays alongside the 3.5" bays - professional Serial Attached Scsi (SAS) drives run around 15,000 rpm and have 150gigs in a 2.5" form factor - the rackmount systems i work on are generally packing a raid5 of such drives
www.solidstatedigital.com.au will have every solid state drive available for consumers. I bought my aftermarket runcore 32gb ssd for my asus eee pc from them, and theyre a bunch of top blokes - i personally will be buying 2x60gb SSD OCZ Vortex when windows 7 comes out and I can buy a copy, then installing them as a raid 0 array for a total of 120gb, with a raid1 mirror of 2 gigs (2x2gb wd blacks)
-D