I've looked at several sources including Bloomberg, Zacks and Cap IQ. Many times, they don't update their data with the revisions. I'm looking for Income Statement and Balance Sheet data going back to 1994. Who has the best data?
If you really want accuracy, the answer is the SEC.
Otherwise, you'll have to expect some inaccuracies. Bloomberg I would probably rank highest of the ones listed, but this is more qualitative than quantitative, as I know of no studies that suggest it to be most accurate.
S&P Compustat is the standard for most academic research.
I believe, that Bloomberg and Factset provide the most consistent data set out there. However, their solutions are quite pricey (unless you already have access). A friend of mine is working on a similar solution, which is offered for free. Check it out under www.simfin.com
Update 30.07.17: So he has just updated the site and now standardized company statements for over 2000 US equities and financial ratios are available (all based on SEC data with free download). If you are looking for a bulk data download feel free to reach out to him.