Laptop or Desktop for gaming?

I'm not a hardcore gamer or anything so about all the games I'll be playing is MineCraft and I'll let my brother download Wizard101. And I'll need to type up papers for school and make powerpoints. And then useing the Internet, but that pretty much sums it up. However, when I play I hate when it lags (who wouldn't?) so I want to make sure that it doesn't. So which is better and why? Thanks! (And when I go to my dad's house a laptop would be nice.)