It would be hard to say because a true iPad version has yet to be released. The iPad experience right now only uses the amount of the screen that would be displayed by an iPod touch or iPhone.

I would guess that when a true iPad version is released, it will have more functions, such as example sentences, that currently cannot be displayed on a smaller screen.

An iPod touch is less cumbersome if you plan on practicing for an extended period of time.

I'm using an iPhone and I love that even when standing on a moving bus, and holding onto a handle, I can still just use one hand to hold the device and input words. I'm not as fast as Nick with thumbing in characters, but it works well enough.

I'm using the iPad. I like it; it's definitely sexy. I had bought an iPod touch, but took it back the next day; it was too much like a duplicate of my phone (which is android).

So the iPad... I do it at 2x size and I use a stylus for characters (I'm finding I'm using the stylus for everything, actually).

Three things I noticed:
1) when I skractice, I usually read the small font at the top of the screen, rather than the giant character that takes up the whole screen. It's... too big to look at. I am aware of how crazy that sounds.

2) the iOS version prompts you with pinyin, english, and audio. I've become aware that my eyes are drawn almost invariably to the english, in a way that wasn't the case with the online service. It bothers me, I wish I could turn the English off and look at a helpful, level-appropriate sample sentence instead.

3) I adore the dark theme. Adore. But I don't use it because after prolonged use my eyeballs start to invert themselves.