Wrong place to post this - use the 'what cube should I get' thread. Mods will move this there, no doubt.
anyway, neither is 'better'. The Zhanchi is perhaps the faster cube, but both are capable of getting you sub-7 times, in theory.
What do you like in a cube? Some people would argue that the Moyu Weilong or Fangshi Shuang Ren are superior cubes to any Dayan cube, but some people still think the Zhanchi is the best cube around. In the end, it comes down to personal taste, so what 'feel' of cube you like should influence your decision.
If you're looking for a cube that will make you faster, then stop looking. No cube will make you faster, only practice.