sadly, Arteta... I know his form is a cause for concern but I beleive he'll return to form sooner rather than later. however because he is the oldest and highest earner of the 4 u listed, he'd have to go (I also think he'd fetch the least, especially w/ his wages too).
To sell Fellaini would be crushing, he's the most important player we have now.
As for Baines, he'd be the hardest to replace imo, as its very difficult to find a half-decent left back, never mind one of the his calibre that is not just defensively sound but also has a huge impact on our attacking play.
Rodwell is still a bit-and-pieces player to me at the mo - he has all the attributes needed to become a top, top player but they haven't yet formed to produce one. However, when it does click with him, he's going to worth a hell of a lot more then now, so i wouldnt consider selling him now.
I dont really want to sell any of them tho tbh!