Hmmm... well now if u still want just one line opinion then simply speaking my personal view is Cracking CAT (or to enter IIM) is more tougher than CA Final.
And now if you want to go through my thoughts on this then read ahead.
Remember in CAT there is no pass or fail. YOU will get some percentile and if yuo manage to get into a institute of your choice then you are pass and if u dont then u r fail no matter how high your percentile was. Unlike CA exam, CAT dont ask for any professional or specialised knowledge of any field. If u go through the CAT questions you will find that they are maximum upto graduation level. In Quant (maths) they ask you conceptual problems involving concepts of ratios, speed/distance, proportions, probabilities etc. Similarly english consists of vocab., reading capability, verbal questions etc. and DI contains analytical reasoning, logical questions etc.
U just pick some CAT based sample paper and try solving it just for fun i.e. without exam point of view, and you will find that even without any preperation, and just with basic knowedge you got upto graduation you can sort out many questions of all sections yourself just based on simple logics and reasoning. Thus CAT question structure is much simpler than CA Final and I feel that this simplicity of CAT makes it more tougher than CA. U see being simple is not so simple.
CAT is taken by student of every stream i.e. commerce/science/arts, hence paper is structured so as to give equal opportunity to everyone. They will not ask a question on amalgamation or a question to form chain reactions or how plants/animals reproduce.
They will simply put a question like - Ratan, Anil, Pinku and Gaurav are brothers of Rakhi, Sangeeta, Pooja and Saroj (not in order). Each boy has one sister and name of brothers and sisters dont begin with same letter. Pinku and Gaurav are not Saroj's or sangeeta's brother and saroj is not ratan's sister.
Tell who is Pooja's brother???
Now whether you are a ca or an engineer or a doctor or whether you were a rank holder or a compartment holder is not going to make any difference to solve it. You just need some logical calculation to get the answer. In exam you will have some seconds to solve it. Some will sort out in just few seconds, some may take a minute and some might leave it.
Hence i feel that showing our natural or simpler logical and analytical ability can sometimes be more difficult than being a highly complex professional. Not just CAT, i feel every competitive exam right from recruitment of a clerk to recruitment of an IAS is more challenging for me than a professional exam.
We all always hear that CAT was tough this time or easy and every mba student keeps on talking about CAT, but once CAT is through, you get admission to MBA, we never hear of how were the exams of MBA. Whenever we talk about IIM we go directly to CAT but we dont discuss how was the paper of IIM i.e. the semester or final exams of IIM students which they appear for getting their degree, bcoz those exams become professional i.e. for a MBA
And let me tell u that going by same reasoning which i have given, someone can also conclude that competitive exams are more easier than professional one as its more simpler to show your general reasoning ability than to show professional one. It just depends...Hope u understand what i m trying to say!!!