I prefer Borgnine's portrayal as I think he humanized the character more so than Steiger. Again, the movie flushed out the characters more, with better and more extensive writing as Borgnine had more to work with than Steiger. Another thing, as an actor, I think Borgnine could probably handle...
Not me, after spending time this weekend watching the new Kino Blu-ray twice because of the audio commentary and then watching the 2009 Criterion "Golden Age of Television" DVD again, I prefer Borgnine's portrayal of Marty. IMO, Steiger was too harsh and anguish in that role. With that said...