Its a personal preference. The G2 accepts more accessories where as the Zeus RIS is based off of the g1. If you wanted to totall mod out a pistol I would say go with the G2, if its a side arm stick with the g1.
You can still attach a flashlight kit the G2 and have a G2 RIS!
Flashlights are only good for night games or intimidating looks. Consider that as well.