Have also a look at this: http://www.nature.com/nmeth/journal/v12/n4/full/nmeth.3312.html

The system from Church lab is also very potent with a small difference that it is a bi-partite system in contrast to the three-partite system from Zhang lab.

Another difference is that the third trans-activator domain is not the same (both have p65 and VP16-based TA): HSF-1 for Zhang system and Rta for Church system (from Eppstein-Barr virus).

Since the Church system is composed of less components, I would first go for this.

Thanks for the info. I am going to try it out and see how everything goes.