Would iOS developers be better served investing in QA over unit testing?

FWIW, whenever there's a budget for it, we try to do both. Unit testing and QA testing address two different aspects of software development; unit tests validate that the individual parts of your software work well, and encapsulate the developer knowledge that went into building them. They lower the cost of documenting the code, and make updates and improvements easier to maintain—as I like to think of them, they create a cocoon of safety in which a developer can introduce change without having to worry about the consequences. QA testing, on the other hand, validates that a software is ready for production by answering the question “from the point of view of the user, does the product do X, Y, and Z?” All the unit tests in the world aren't going to answer that question, because they're concerned with the individual pieces of your software, and not with the way they interact together to create a working product. (Incidentally, QA testing can answer the question asked by unit tests, but, whereas the latter run automatically, QA must be done by hand, which makes it slow, expensive, and imprecise.) So, to more directly answer your question, in my experience: Unit testing is a future-looking investment. A proper testing harness ensures that your developers are freer to focus on solving new problems because they don't have to worry about stepping on the toes of the existing code. As a bonus, it encapsulates the assumptions that developers make when they write the code, reducing the cost of documentation. QA focuses on whether the product in a given state is ready for prime time. Unlike Unit Testing, which is a tool that is useful for ongoing development, QA is something you do only when you think the software is ready to go. In other words, a unit test failure is expected—which is why unit testing is largely automated—whereas a failure in QA means you've wasted your tester's time with a product that is not ready. That said, if I only had a choice between one or the other, I would pick QA over unit testing—but I only do so when I absolutely cannot convince a client otherwise, and I fully expect the overall cost of a project to be higher in the long run because of it.