Many experts will tell you that the maximum reward is gained from finding bets that offer real value. For example - bookmakers love long ACCAs simply because it is so hard to generate a consistent profit from them so steer clear of such bets.
If by ACCAs you mean parlays or a bet consisting of multiple choices it can give you the maximum reward but this happens only a few times and you need a big amount of luck. I have seen people though win a lot of money from these parlays when they happen.
I have some fan pages in facebook which I follow and they like to place accumulator bets, they don't hit it almost never but there are a few cases when they do and the reward is something like 10 Euros for about 4000 Euros. I just follow their bets with 1 Euro when I don't forget to do so. Never hit one though during all the time I have followed them but I am not a regular follower.
Hence what I said - bookies love punters placing these bets and why they often give extra incentives on them as they very rarely come in.