Get the CS series because it's built better. If you check Corsair's website you'll see that they make the power supplies units for different categories of PC builds. Now it depends what your future plans are for your PC, what upgrades do you plan to make. I recently bought a RM750 and i'm happy with it. I chose it for the 5 years warranty (the CX and CS series have 3 years) and because i don't want to worry about the PSU anymore in case of an upgrade. So, between the CX and the CS i strongly recommend the CS, or a higher class from Corsair. As far as i know, many of Corsair's PSU's are actualy made by Seasonic and this is another thing that convinced me to go with Corsair for the power supply.