There really is no "easiest exam." While the exams are all curved, the grading is adjusted to the perceived difficulty of the exam by the test writers so that the passing rates are all "balanced" and the rating percentages should be about the same in a perfect world.

FAR-While it's the most material and has calcuations, you don't have to have a great percentage correct to pass, or have a high score. Think about this as that class that everybody hated, but the professor curved enough so that you could get a 60, and still have an A. You'd probably do better in this section if you did better in your Intermediate and Advanced classes, or work as a staff accountant or auditor.

AUD-Not as much material on this exam, and no calculations.  Although, this exam gets a lot of people because of the tricky questions, and the dull as paint subject material.  You have to get a pretty high score to pass though, because there isn't as much material, and no calculations. You'll probably do better on this section if you did well in your audit class, work in auditing, or are more linguistically inclined.

REG-A lot of material on this exam, although not as much af FAR.  Additionally, while there are some calculations in the tax part, there is not much otherwise. However, it is aggresively time sensitive.  You don't need to get as high of a % correct to pass this one.  You'll probably do better on this section if you did well in your tax classes or work in tax.

BEC-Often seen as the "junk-box" of the exam. Not as much material as in other sections, but some people seem to have trouble with it because they blow it off, and don't spend as much time studying on it. In the last few years, it has had the lowest passing rate, and that is mainly attributable to the fact that you really have to nail it to pass. When I see somebody with nearly perfect scores on the exams, this is always the one with the lowest score. However, I was an odd case, where this was my highest by far.  This is a section that  you'll do better on if you're more Finance, Economics, or Cost Accounting inclined, like if you work on Wall Street, are a computer programmer or do better in your Finance and Econ classes.