I do back-end development, front-end design, and fashion photography.

Backend engineers are paid more. It's a cultural bias in software development that the front-end or "gui" is what the "graphic artists" creates, while the back-end is where all the complex computer science theory needs to take place, and should never be questioned.

The reality is that design shares techniques with art, but is not art. Good design solves a valuable problem for the customer. Good art is a unique personal expression. You need to be a design professional to judge a design, because otherwise you lack the technical training to correctly judge it. Analytics can help define if a design is well made to a degree. For example, if a visual redesign increases customer signup, then it's well made. The specifics of aesthetics, and colors aren't as important as information hierarchy, visual contrast, and ease of use.

With the advent of AngularJS, EmberJS, and Backbone, front-end development is equally complex compared to back-end development. I've used 8 different PHP frameworks since 2001, and recently Flask with Python; against MySQL, PostGRES, and recently MongoDB. The programming complexity of the front-end is more complex, because on the back-end developers can rely on tried and well-worn programming design patterns from the past 15 years. On the front-end, we'll create entirely new interface paradigms that didn't exist 3 years ago, such as side-swiping on websites (borrowed from smartphones and tablets).

I personally find front-end development more complex, because of the constantly changing visual design. Back-end development is moving more towards RESTful API and Service Oriented Architecture, which is comparatively easy, and doesn't change as quickly. The back-end often supports a single OS, single DB, and a single language. The front-end has to support 12+ system configs of browsers (IE, Firefox, Chrome) and OS (Windows 7, Windows 8, OSX, Ubuntu, etc.). Ironically, the front-end is what paying customers spend the most time with, but the people creating it are generally not given the same level of respect as the back-end developers.