I have to agree with karistouf, because Fantastick is my favorite app right now for creating remote interfaces. If you want to create a complex interface as quickly as possible, Fastick may be the way to go.
However, if you don’t need the ability to push programming logic to the device, image support, layouts generated in real-time, and you don’t need anything more complex than the controls included with TouchOSC, then try TouchOSC. I would rate them:
TouchOSC - very easy
Fantastick - easy
But it’s not just that TouchOSC is easier, it’s sliders are very pretty and are native so they are very responsive and fast.