I don't know why you'd search for this answer, or ask anyone but yourself, because there is no correct answer. Ignoring the fact you didn't give nay drive details, you and only you know what you will be installing on the PC, in terms of large games, applications, etc, along with the general purpose of the computer. That will tell you the answer.
Yeah I decided I am going with a SSD 40GB drive. Lower failure rate, and faster. That should be enough and I will put the rest of my data on my 4 (500gb) HDD. Should be perfect.