C rating refers to the amount of amperage the battery can put out.

think of it like a facuet. the water is always under the same amount of pressure(like the same voltage) but depending on how much you open the tap changes the amount of water you get.(more amperage)

if you used a 2s 10c 3500mah lipo(dont, just an example) and then ran a 2s 30c 3500mah lipo you would notice a gain in the acceleration. the initial burst of energy that the higher c rated battery can put out increases performance.

and yes, higher is better. go for ones that say 30-40c.