I think both grippers can be suited for this application. However, as there are many, many variables into the equation, I don’t know which one would be the best.
– Gripper 2 clamps are always parallel, and it can be quite precise.
– Gripper 3 won’t be precise but maybe allows you to increase the picking success rate (I’m not completely sure, needs testing). Also, if you have a container with many objects on top of each other, Gripper 3 will have a better success rate than Gripper 2.
For the slippery problem: Both grippers have anti-slip rubber. If you need better adhesion to the objects you pick, you can easily add something else on the gripper.