I play both and I'm not very good at either. I very much prefer cash, but a tournament every once in a while is fun. And i just found a new love: HU sng's.
They're all immensely different. I prefer cash because there are so many ways you can play it (In an amateurs mind there are endless possibilities )... The players determine the action and not the stacks and blind levels.
In tournaments I feel like most of the time there is exactly one way I can play a hand... The longer I play the more it feels like I'm a slave to ICM.

I think what helps my game is playing both at the same time - one sng table and 3 cash tables is a good mixture for me because I take a bit of my tournament mentality to the cashgames which prevents me from going apeshit against über passive minbet donks.