I did AUD before FAR, but that was mainly because I've been working as a governmental auditor for the past 2.5 years (at the time, 2 years), and I had just taken an Advanced Auditing course over the summer (in order to hit my CPA requirements), so I figured it would be the easiest section for me, and I wanted to start off strong.
Fortunately, I was right, and AUD wasn't too bad for me. The FAR based questions I got weren't too bad (at least I didn't think so), but obviously, others have claimed they were cursed with difficult FAR based questions.
I have heard the same thing that it's better to start off with FAR, since it bleeds into AUD, and you get the “hardest” (as far as amount of material) section done first before your 18-month clock starts. But obviously, it's not a rule set in stone, and I don't think the same order is right for everyone.
I ended up taking FAR immediately after AUD as my second section. Unfortunately, that was the only section I failed on my first attempt (I think had I given myself a little more time to study and not panicked at the insane SIMS I got, I would have passed). Retaking FAR tomorrow and hoping to be done with all this.
AUD - 85 (8/30/2015)
FAR - 73 (10/13/2015), 85 (2/29/2016) (AND DONE!)
BEC - 83 (11/04/2015)
REG - 81 (11/30/2015)