How to choose the offer of the two companies?

This situation is exactly as you said, there is no best way. Generally, formal enterprises will sign agreements when they enter the job through interviews. If you accept the Austrian enterprise first, you will definitely be informed to go to work in a few days. If you go, you will definitely sign the labor agreement. If it passes the German enterprise, it will involve breach of contract. In addition, even if you don't sign an agreement, it's not good for you to go to an Austrian enterprise and a German enterprise within a few days. Foreigners are very honest. Maybe you won't have two jobs.

In addition, if the second interview in Germany is not long, the best way is to find an excuse to stabilize the Austrian company first (I guess it is a bit difficult). If it really doesn't work, I want to work in Germany and get better treatment. Then weigh your success rate in re-examination in German enterprises. If it exceeds 50%, it is worth fighting for and giving up the opportunity to go to Austrian enterprises. I have been in charge of enterprise recruitment for these years. As said on the first floor, a formal interview is generally more likely to pass the second interview, so it is good to play your due level. As the saying goes, "I can't bear to let my child catch the wolf", sometimes we still need to make a decision. Finally, good luck! O(∩_∩)O~

Supplement: When did the German company inform you of the interview? If you directly tell Australian enterprises to consider between the two enterprises, the other party may not accept it, even if you are given an estimate of the consideration period, it will take about 3 days. If you go to an Australian company within 2 weeks, the German company will inform you to go for a second interview within 2 weeks. You can go to an Australian company first. Personally, I prefer German enterprises. Personally feel that the development platform and treatment are better than those of Australian enterprises.