Australia simply have all bases covered. True all-time great levels overall for spin, pace, and batting, and two serious batting advantages in Bradman and Gilchrist. The only questionmark is their opening pair, but that is offset by the rest of their batting lineup.
The other teams have their own serious chinks. West Indies lose a lot of their bowling fire power with Sobers and Gibbs coming after the three quicks. If they had a fourth paceman like Garner or Roberts instead of Gibbs, I would put them on near level with the Aussies.
SA are underrated, with batting up to 9 and 6 bowling options, but quantity doesn't necessarily make up for quality, and they seem to lack cricketers who can really stamp their presence.
Pakistan have the best pace attack, but their middle order is a bit shaky against worldclass attacks, and lower order pretty weak.
England are wild cards. Petersen shouldnt be there, but the batting is very strong overall. The problem is that there's questionmarks around Botham, Larwood and Barnes on how they would consistently perform and in what conditions, while the spinner is not known to bowl great outside of uncovered wickets.