SSD or HDD for DAW setup?

I'm looking into improving efficiency in my production setup by installing either an SSD or an HDD. My tech specs will be below. I don't know which to get. I've heard that SSD's can be faster than HDDs but they only load up the samples fast and then the rest is on CPU & RAM. Which would be the best investment? Also, would it be easy to get all of my sample libraries onto whichever device or would I have to reinstall them through some complicated process? Thanks for the help.

Here's my computer's tech specs:

iMac

21.5-inch, Late 2013

Processor 2.9 GHz Intel Core i5

Memory 8 GB 1600 MHz DDR3

Software OS X 10.9.4 (13E28)