I like Scott Steiner a lot but a return to WWE would be a bad choice for him. His last WWE stint was easily forgotten, and this time could be even worse. He made it a habit of his to just badmouth pretty much everything having to do with WWE. He's 46 years old, and even though he can wrestle better than others would at his age, but he's not going anywhere if he ever were to return.
If you put all that aside, and WWE and Scott Steiner does reach an agreement, surprisingly. I say he should go to Smackdown. ECW would do absolutely nothing for his ego. He's be there to put over people, but I'm sure he'd get tired of that after a few too many losses. Raw still has Triple H, and now John Cena and Randy Orton are bigger stars now, compared to when Steinter was last in the WWE. Plus, he would probably put a damper in other mid card pushes, such as Kofi Kingston, Jack Swagger, M.V.P., Mark Henry, Chris Masters, etc. So, Smackdown would be my choice. He could fued with the likes of Batista, Rey Mysterio, The Undertaker, John Morrison, Finlay, etc.
But, that doesn't matter because I'm sure that Scott Steiner and WWE will most likely never reach any type of agreement resulting in a return.