Paddles come in a variety of thicknesses ranging from 8-20mm, and it's not uncommon to see two different thickeness options for the same paddle. There are some general rules of thumb for choosing the right thickness paddle for your game, 

but it's important to keep in mind that there are some exceptions.

Thinner - Thinner paddles typically have more "pop" or rebound which is why many manufacturers will call their thinner options "power paddles".

 They often have a smaller sweet spot and can be difficult to control if players are unable to find it regularly making them more common choices for advanced players.

Thicker - Thicker paddles tend to distribute force more evenly and make controlling the ball easier. 

They have a more even sweet spot across the face and slightly less rebound making shots more predictable. 

Players who want more forgiveness or are looking to improve their game often choose a thicker core paddle.