What does it take to figure out which Fortune 50 is the best tweeter? Apparently, an undercover spy and a little bit of consumer-oriented tweeting. A new study looks at the top Fortune 50 companies on Twitter, and shows how a little experimentation can uncover a lot of facts.

The digital agency IQ sent out tweets to companies on the Fortune 50 list to see who responded best, and how companies can craft better Twitter presences [here's a PDF of the full experiment].

As the report explains, the undercover tweeter sent out @mentions to each Fortune 50 on Twitter. They then took a look at who responded and how.

Out of the Fortune 50 group of companies, 16 didn’t have a Twitter account that the authors of the experiment could find. Of the remaining 34 that they did send a customer support question to, 23 responded.

How fast were these big name companies at responding, when they did respond? Fast. Very fast.

General Motors responded in 2 minutes, UPS took 3, and Best Buy took 4 minutes to pen a 140 character answer. Not bad at all.

And several companies either redirected the customer service tweet to the appropriate account, or asked to move the conversation to direct message when appropriate.

So what were some of the takeaways of this study? I’ll let you take a look for yourself, but one that I found most interesting was to clearly identify who you are and how you are associated with the company in question. Even a big brand like HP can sometimes mess this up, sending a message to a customer from an account called “Jeff” rather than their HPSupport official account.

There are a few other choice takeaways that make this report worth a read, so check it out here [PDF].