I would say a rough estimate would be:
Liverpool
----------Reina
Kelly--Agger--Carra--Enrique
Hend--Gerrard--Lucas--Downing
------Suarez--Carroll
Doni, Skrtel, Johnson, Adam, Spearing, Maxi, Kuyt
Others: Aurelio, Coates, Shelvey, Bellamy, Flanagan, Robinson
Arsenal
---------Chesney
Sagna--Verm--Mert--Santos
-----Wilshere--Ramsey
Walcott--Arteta--Gervinho
-----------RVP
Fabianski, Djourou, Gibbs, Song, Arshavin, Benayoun, Chamakh
Others: Diaby, Koscielny, Rosicky, Park, Chamberlain, Squillaci
Regardless of what you think of my choice of line up, I would argue Arsenal have more strength both on the bench and outside the match squad. Players like Benayoun and Arshavin would be more likely to turn a game, imo, than Adam or Kuyt. And whilst Arsenal would struggle to replace RVP if he was injured, I think Liverpool would struggle much more if Downing or Suarez were injured as they are crucial players with no real replacement available. Liverpool have a stronger first XI, but I think overall the two squads are of similar quality and it will not be easy for either of them to be certain of 4th.