Double or Single?

We were planning on using a claw that would be actuated by pneumatics. The problem is that were not sure whether or not to get the double or single acting cylinders. The pneumatics will push a 500gram claw. It will be hooked up to two reservoirs. It will be our first year doing pneumatics so we can use any advice.

Buy double even if you need single acting features.

This way it will future proof your purchase. As a double acting can be used as a single acting by adding rubber bands to it and plugging a hole in the solenoid so you use about the same amount of air as a single acting would.

For a claw it would also be beneficial to save air on the opening. Another thing is double actings have a shorter overall length due to the spring in the single actings

How many uses do you want out of this?
Doubling acting pistons will use double the amount of air per claw grab so that should be the deciding factor in which pistons to buy.
For competition teams I would agree with Kyle that Doubling acting is better but if you want to keep this robot together for longer than you might only need single.

I want probably want around 15 rounds (open plus close combine to make a round) and we also have a transmission on our lift which needs about 2 rounds. This piston can be double or single but most likely single. It will be attached to a 36 toothed idler.

In general, double acting pistons are more useful. As Kyle said, I would suggest double acting pistons even though your application seems to only require single acting pistons.