Hi whatisthematrix,
You ask a good question; there's no "one size fits all" answer though. Since many GMATers have issues with fatigue - especially later on in the Exam - it would probably be best for you to start with the Quant and Verbal first (in one order or the other). Doing some 'warm-up' practice questions (for example, during breakfast before you leave for the Test Center - or begin your Exam, if you are taking the At-home GMAT) is a good way to get yourself in the proper Test-taking mindset.
Some GMATers prefer to start with their 'stronger' section, so that they can build up confidence before facing the second section. Others prefer to face their 'weaker' section first, when they are more alert and have more energy. Thankfully, you can "test out" both options during your studies. Many CATs/mocks now offer the 'section order' option, so you can experiment a bit and decide which of the two options is better for you.
GMAT assassins aren't born, they're made,
Rich