Thanks very much for your advice, everyone. I still think I will attend the AC at Accenture for 2 reasons:
1) I'll get to see some people I would work with and be able to assess the general atmosphere at ACN (and how you're treated). If I feel I don't fit in there -> no regrets!
2) If I apply to ACN later in my career, I think it can be beneficial if their records show I passed their AC successfully some years earlier. On the other hand, they might not appreciate the fact that their records show I turned down their offer (if I get one).
I really think I will enjoy working at Deloitte, it's just a matter of being 100% sure I made the right decision. From the very beginning I thought Deloitte was the company I wanted to work for (among the Big Four). Later, I applied to ACN, just in case I didn't get through Deloitte's AC.
To be more specific about financial rewards, ACN is far more generous on bonuses, less on basic salary. I just don't like the idea that at Deloitte, you need to convert your cash bonus into flexible bonuses (i.e. private medical care, more holiday, etc.) where the same bonuses belong to your core benefits at Accenture, for free!
So, it would be great if so. could tell me how the core salary evolve at ACN and Deloitte. Because after 2 years at ACN, your £10,000 bonus is gone and you're left with a lower basic salary than Deloitte, I suppose...
I don't want to sound superficial (always talking about money), but as a young professional, if these 2 companies offer the exact same career prospects, then the decision comes down to a financial matter!