ACA is considered a bit harded than ACCA generally - plus the pass mark is a bit higher 55% vs 50%
The major issue though is that you get sent to class for a few weeks and have to learn and remember a vast amount of information in a short period of time - plus balance study with work etc.
The content is no harder but you need an extra 5% to pass so it could be deened slightly more difficult.
On the flip side, I believe that there are 6 computer based exams v 3 with acca, so you're effectively given an extra 3 easy passes. For computer exams, read 'easy exams'
There is little that is that intellectually challenging in the ACA. There is just a lot of it. Of course you have to be reasonably intelligent but really, most of it comes down to being able to graft.