It depends on many factors. But I will focus on the visa part.
As long as you are in H1B, you have a big clock ticking down. If you cannot get to late stages of the Green Card application in the maximum 6 years of H1B, you cannot stay in the country.
So if you want predictability of your ability to work and stay in a country, a real shot at PR in Australia would beat the situation on H1B, which has some out of your control stuff.
None of the two options prevent you from getting to the next one in the future; in fact, if you haven’t applied for a Green Card and particularly if your current company has no plans to offer it in the short future, it could probably be good strategy even for long term in the USA to go to Australia for some time and then return to USA on H1B (maybe in the 5th year, so you may still be cap-exempt but with more time remaining).
Other factors that would be important would be:
– Professional: depending on your field, you may have better opportunities on one or the other
– Closeness to family and friends: I am Mexican so US is closer to my hometown; for Indians or Chinese, Australia would be probably better in this respect
– Salary vs. living costs, which should be analyzed at the city level, instead of country. Similar salaries in San Francisco, Sidney, Austin or Perth would provide you a very different level of savings, for example.