Both devices are great the only choice you will have here are the games. In terms of 3DS games they're more geared towards actual gaming since the hardware itself is designed to play games while the iPad is, well it's a tablet and although you can play games on it pretty well, nothing beats the old school physical buttons and sticks. If you want a wider range of games then I guess you can go for the iPad since mobile games are really all out there be it a bit of a copycat market. If you want more immerse and a more solid gaming experience go for the 3DS.
It's all a matter of personal preference to be honest. A 3DS does have a wide variety of games to choose from, in person and in a virtual store. A iPad however, offers games and other features. These features surpass the options you have with a 3DS. So I recommend buying an iPad for both gaming and for your lifestyle.
