I use Hannah for alk and Salifert for everything else. I think there are very good arguments for going with Hanna for alk--the test is a quick, simple procedure, and it is notoriously accurate. It's also nice to get a number estimated by the device rather than a color chart that you have to squint at and make a subjective guess at which shade is closest. For everything else, I have a vague sense that Salifert and Red Sea tests have a better reputation than API, but opinions vary. At least one person has done some comparative testing, although I don't believe those tests had the benefit of a gold standard. There seems to be at least somewhat of a consensus on the Hannah alk test.