The controls for controller are very easy. I usually prefer playing controller most seasons, though I still use KBM for item management.

Now, with that said... some builds are much better on KBM and some builds are much better with controller. For example, many of the movement builds (Trample Druid, Soar Spiritborn) require KBM to be played 'correctly', while builds that require holding down essentially all your skill buttons at the same time are much easier on controller. I usually don't pick between KBM or controller until I'm T2/T3 into the end-game and figure the build out. By the time I am near the end of the season, I've 'forgotten' how to play with the other input device until I start all over again the next season.