It depends on your preparation and availability of time along with your capability to handle both group at a time. As per my understanding one should go for single group. My suggestion is not baseless and based on long term professional success and further supported by the following points:
1. By giving one group one can fully concentrate on true and expert examination preparation.
2. By giving one group one can fully utilize his/her time and gain full knowledge of course.
3. According to me group clearance is not the only parameter of success.
4. By giving one group this time one can arrange some time for himself/herself which is very important. Self assessment is also important.
5. Appearance in both group is not a guarantee of success.
These points are based on my personal thinking and helped me a lot in my professional exam preparation and prevent me from failure along with good application of my knowledge.
I personally feel that a reasonable distinction is required to be drawn between quick success and long term professional success with good knowledge.