Probably the most asked question... so here goes..
My short answer is APM and AAA :)
My long answer is...
Technically the most difficult paper - and this is backed up by the horrendous pass rates.
It builds on FM but is about twice as tough.
If you don't work in this area then you will find the concepts hard to grasp. However the questions do repeat themselves so super hard work on past papers can get you through.
Like all papers passable - just beware of the technical level of difficulty here.
Very strangely (to me, at least) it also has a horrendous pass rate. It must be said acowtancy pass rate is much better and I have a feeling it's because we don't offer a textbook on it!
This then forces students to watch the classrooms and take the advice therein and not able to overstudy it. Overstudying the knowledge here is a problem (like with SBL) - missing the fact that it's very much an application to the scenario based paper.
My advice - read the examiners reports after every past paper that you do.
The problem with this paper is the sheer volume. If you go and have a look at the ACCA website now and download the syllabus - you'll see most of TX specifically referred to - hence making it almost 2 papers in one.
This creates its own problem - as students get lost / demotivated and have little time to recap their knowledge and hence go in the exam feeling under prepared.
That said the examiner is reasonable and not as tough as say AFM.
Do this straight after SBR. It's basically auditing SBR!
The problem with this paper is the examining methodology. She wants you to use the scenario, but also give great depth to your (many) points.
In my experience, students quite enjoy the paper - and feel prepared going in - and the exam is very stable - BUT the issue is time pressure.
With all those points and depth and scenario to use - students find themselves running out of time. This is true of this paper more than any other in the ACCA.
The trick is to use your allotted time for each question and move on.. no matter what. That means you get all the low-lying fruit - the easy marks - in every question.
So there you go. Personally I prefer APM and AAA but we are all different - just beware of each of the papers idiosyncrasies - and these are best learnt through my advice in the classroom and backed up by the examiners comments in the examiners reports.
Hope it helps and good luck with whichever you choose.