Well, Sebastian Shaw once beat up Rogue so badly it was ridiculous. Beast had to step in, and he paid for that by having all his bones broken. It was at this point that Psylocke decided to play savior, and for her efforts Sebastian Shaw killed her!
Thus, Rogue would be out of the fight since she basically could do nothing to Sebastian.
Parasite is an interesting character. At his max (as in when written to maximum capability) he has the ability to siphon energy from the best. However i doubt he'd be able to take down Shaw before Shaw took him out.
But that would be interesting.
However Rogue would be a non-starter. He literally wasted her and the other X-men, telling them that he was basically the true evolution of mankind and that mutants were nothing more than an abberation (he claimed that he was no per se a mutant, but rather the next stage of human evolution. The 'true' homo sapiens superior. And that mutants were basically just an evolutionary sideshow while he was what was to come). Whether or not Sebastian was hallucinating, one thing was clear.
He b!tched-slapped Rogue as if she was some pip-squeek schoolgirl.
He broke every bone in Beast's body, and he would have died had Sage not acted as a catalyst (which sped up Beast's natural healing factor - he has one, it is just weaker than Wolvie's - but in the process made him become more feral in appearance. That is where Beast's current 'look' came from).
And he killed Psylocke, and then stuffed and mounted her body!
I'd say Sebastian takes this. He can take anything the others can dish out, and he can use that to dish it back to them.