I'd say apply directly to the firms you are interested in - it can slightly increase your chances as it's cheaper for the firm and shows that you've put some effort in to thinking about it. As a new ACA, you probably wouldn't join a strat firm at the same level as a top MBA, but you don't need to get an MBA before applying; some are definitely in the market for your skill set right now. What would they look for? A (very) good degree, demonstrated relevant experience, analytical ability and commercial nous, mainly. Good luck!