SSD all the way. Access times are <0.1ms.
Even with 2 SATA II HDD in RAID 0, and SSD reads can be up to double the RAID array.
A test was done once that did show that 4 x HDD in RAID 0 actually beat a single SSD. It was done with drive striping, so drive use was optimized, but not using the complete drive size (i.e. they partioned the array to only use the first 100GB (?) of each drive, 400GB RAID 0 array, which is the fastest part of a HDD). But, this was done with "older" drives, as the new Seagate 7200.12 and Samsung Spinpoint F3 are faster now.
Still, my RAID 0 arrays showed my SSD array at reads over 300MBps, and my HDD array peaking at 150MBps. (BTW: I only RAID'd my SSD due to their size, I don't recommend thii to a newbie.)
I just picked up an OCZ Agility 2 60GB SATA II SSD for $139.99, with a $20.00 rebate coming. This is only a little more than 2 x HHD at 1TB+. This drive has the new SandForce 1200 controller, with read/writes around 285/250MBps.
You loose size, but gain speed!
BUT, write speeds can be less with a SSD. But once the OS is installed, reads are were it at!