Are you talking about the opictal drive? Or Solid state drives vs standard hard drives?
If we are talking storage.
SSD's have amazing read/write speed. They are super fast, no moving parts, so very low/no noise. Small, but normally sturdy, and easy to mount.
The cons to a SSD (currently) They are costly. In japan I spent $217 USD on a 128 crucial SSD. You can buy them a bit cheaper on Newegg.com. But the space/cost rate is very lop sided.
So the best idea for SSD's is use it for your OS, and a few primary programs you use. Try to limit the games, music, and movies on the drive. As your space will vanish VERY fast. Just my OS, 1 game I'm currently playing, and my primary programs chewed up about 32Gb. I route all my downloads to a 7200RPM HHD. So it works out ok.
On the note of HHD's. They are pretty dirt cheap now. A TB of storage costs less then $100 these days. Which makes them amazing for a cheap build, but getting great storage amount.
They are not nearly as fast as a SSD. 7200RPM drives are nice. They read/write at a acceptable rate for modern games. You will notice a decrease on game loading vs a SSD. But they are a good method that most uses still use.
Overall though, my opinion is this. Buy a SSD atleast a 60GB for your OS, then have a 1TB slave for your downloads, movies, music, and games. Your OS will allow you to boot fast. I sleep mode my PC every night now, and I no sooner punch the power switch and my PC is on.
I hope this answers your question, I was a little confused on how you stated the question. But I hope I answered your question.