Don't forget that some SSD's have a limited (compared to a hard drive) number of writes, called "Write Endurance". This article discusses the issue in some depth. It was certainly an issue with older SSD's, but is becoming less of an issue with newer ones.
An SSD might be more suitable for an OS drive that doesn't change that often, whereas a normal hard drive is more suitable for a data drive that's frequently written to.
If you do go with SSD's make sure you find one with a high "Write Endurance".