They have had different careers and so really you could say both are on a par for their acting styles.
Stalone has had periods of success and then dips only to return to form, but he has a biggger range or roles than arnie and writes and directs
Arnie has a style that is action, comedy or both together and his mastery in such has meant a run of consistently decent to excellent fikms of this genre.
What I wpuld.say is arnie produced more films that are there to go to if you want something to watch in your spare time for stalone their is only a few I rewatch but all are top films