I used a Chi for over a year and they are very good at getting and keeping hair straight.  My hair was starting to feel dry though and I read some great reviews on GHD flat irons and broke down and bought one.  It is the single best beauty purchase I have ever made.  I can not say enough about my GHD.  From the very first use my hair felt silkier and looked shinier than with the Chi.  GHDs rock!