Both are correct, but "seated" is more formal. In normal everyday conversation, and informal or neutral written style, we'd use "sitting".
If you feed them into a concordancer - I used the
Cobuild concordancer - you'll see that the examples that come up for
seated are all from formal written English, for example :
- Ensure the casualty is seated or lying down whilst being treated.
- ... has the necessary space for those seated, whilst retaining an interesting appearance.
- ... such as one of Josef's dreams. Fat lawyers seated stuffing themselves, urging him to eat at the ..
- ...of the British Defence Minister, Mr Tom King seated behind a model of one of the tanks which is ..
whereas for
sitting, while there are still plenty of written examples, spoken examples come up too :
- I mean I know somebody who's you know sitting in a wheelchair after a spinal injury thirty
- That's what your dad says isn't it we were sitting in the car and she lent over and a fag fell
- I'd have a conversation and he'd be sitting on the settee and I'd be having a
- Easy for Warrington. Andy from where you're sitting what a great game Gary Pallister's having