My nephew is 4 and loves the LeapPad. We had the earlier versions when my kids were that age. All the Leapster items have been wonderful!
As for the ds or itouch or iPad mini, I'd pick an apple product because apps are so much cheaper. You can buy so many games for .99 each! Then you just have to weigh how much you want to spend on either the touch or the iPad. We have 2 touches and 2 full size iPads. The kids use the touches and we use the iPads
