@iKlsR I think he was rather correct in asking on the meta first. Good job for that! (even thought his question is off topic.) the part I have a problem with is root answering it there.
@ngoductri It really depends on a lot of things. Blender Internal is faster in the same way that the 3D ViewPort is faster. It does different things. Cycles can be near real-time if you have a couple of CUDA cards. If you don't need the realism, then it might be worth it to stick with BI.
@ngoductri I really like Cycles a LOT... like, a WHOLE LOT... and I think it does any imager (person who makes images) a great benefit to understand Stochastic Photon Mappers, and be able to use one (like Cycles or Octane), but I used the Internal renderer for a very long time, and I can also totally see the appeal of sticking with it.