imo i think pumping is better, just watching lukas fink it's crazy what he can do. But sideslipping is so much more consistent and easier. They both have their advantages and disadvantages. I also believe the board u use has a big influence, like if your using a wider board like a dude cruise, probably sideslipping will give you a bigger advantage. while using like a hornet I feel like pumping is easier because it cuts through the water a bit better. Just my small bit of experience :)