Gordon and Donna were both excellent engineers. However whereas Gordon got a decent job as an engineer without much effort (assumed anyway as we begin the show with him already working as one) the same is not true for Donna who is 'stuck' in a more admin role being somewhat ignored by her boss and at times belittled clearly because she is female.

The main difference between Gordon and Donna is that she has a lot more 'drive' than he. Gordon was happy to settle as being 'just an engineer' hacking away on circuit boards and such whereas Donna always dreamed of more which we see with her character development over the seasons into business management and investment.

There are a few moments where Donna shows more 'outside the box' thinking in solving a problem such as space saving in the laptop they are designing for Cardiff, however I don't think that is enough to say she was superior to Gordon. I always saw them as equals in terms of technical ability but with Donna having ideas far beyond being an engineer whereas Gordon had that 'kid at heart' personality and would quickly lose interest in the higher level managerial aspects. Cameron's character was very similar to Gordon in that respect.

Breaking it down the four main characters have some very interesting overlap. Even Joe had good technical ability but was clearly the more 'visionary' character who used his technical understanding to try new things and push forward into new waters.