Which certificate is the best one for you depends on your own circumstances and situation. If you are preparing for your studies in Germany from abroad and looking to obtain your language certificate from anywhere in the world, the TestDaF, Goethe-Zertifikat C2 or telc Deutsch C1 Hochschule may be your best options.
If you are looking to get your language certificate in Germany, the DSH is a great option. This test is offered at German universities and has got a non-standardized test format, meaning that the university’s teachers create and conduct the test. We find the DSH to be the best option. Not only is it affordable, but due to its non-standardized form, we find it to be a bit easier to pass, as well.