SSD vs Raid is not as easy as sugggested above.
First of all games keep increasing in size, my Bf3 is now 35GB. I am currently using about 400 GB of games. If you want all of those on SSD you have to be a big spender...
Second issue is that games are designed to deal with "slow" hard drives. So you dont really gain much. There are hardly any games that benefit from SSD for load times. In my case only BF3 managed to get a nice boost (2minutes>1minutes) but only on the first map load. The second map is all in VRAM and RAM.
The advantage of using Raid 0 to store your games is that you create a good performing platform for installing your games with the exception of games that use a lot of tiny files (namingly: League of Legends and ALL Valve's games, so DOTA2, Portal, L4D, etc).
SSD is superior as OS drive but you cannot fit your games on it.
Personally I use an SSD OS drive combined with Raid 0 storage for most of my games. Even my old Spinpoint F3 raid 0 reaches up to 250 MB/s during installation of games
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ps: If you are using a hard drive it is important to defragment. Best case scenario you use defragging software such as O&O Software to sort your files based on /name. After that all files of one game will be near each other on the same physical spot. Since your game raid 0 is not the OS hdd it will only be accesing your game files. The result is something called shortstroking which will boost your IOPS greatly. Basically this is caused by the fact that the "head" does not have to much as much.
Note to others: Game load and install times are SEQUENTIAL operations 95% of the time. You can confirm this by checking out your games and the windows resource monitor. Most games package their files into large archives. For example TDU2 has <300 files with 10 GB size. The only exception is for games that do not package properly.