What kind of activated carbon works best?

I went to my local petco and saw 2 different types of activated carbon. One was pellets and the other was more like flakes. Which one is better in a DIY carbon filter?

I would think the flakes would have more surface area and be better. The pellets are cheaper though. Would smashing them up have the same effect as using the flakes?

I was wondering about this as well. In the end I have just ordered 3mm pellets as they were a lot cheaper. Will crush them up if we get a reply on here saying that its better but do know they make a right mess so newspaper down on my girlfriends kitchen table first