Chieftec is by and large poor quality and unlikely to provide it's rated watts (or die quickly if worked hard).  I don't know about MS-Tech, but usually cheap price is a bad sign for a PSU. Zalman makes some decent products and I think that model would be a safe buy. For a rig that is going to be mining 24/7 you will save money in the long run by buying a Gold or Platinum rated PSU. The efficiency isn't as big of a deal for general use with a few hours gaming, but for 24/7 mining under heavy loads the extra efficiency does make a difference.