There's one big, glaring reason to buy Citigroup Inc. (NYSE:C)'s stock: It's cheap.

Actually, the stock is really darn cheap. Currently trading at 0.7 times its book value, Citi's valuation is a fraction of what it was prior to the financial crisis. In 2007, the stock fetched as much as 2.3 times its book value. Rewind to 2003 and you could find the stock trading for a multiple as high as 2.8.

But cheap isn't everything and Citi's stock -- if it's for anyone -- is certainly not for everyone. If any of the three points below resonate with you, you probably want to skip an investment in Citigroup.

You want a top-quality bank It's a common theme no matter what you're buying: If you want something that's top quality, you're going to pay up for it. You're not going to find a Ferrari on the cheap, but you might be able to get a steal on a used Kia.

When it comes to today's megabank landscape, Wells Fargo & Company (NYSE:WFC) is the undisputed king of quality. If there's a Ferrari of the space, it's Wells. And Citi? Well, it's more like that used Kia.

Perhaps today's price on Citi represents a really great bargain on a company that's overlooked and underloved. Or today's price on Citi may represent a reasonable valuation for a troubled bank that still has numerous hurdles to get fully back on track.

I don't think that Wells Fargo will offer the best returns of the banking sector, but for investors who want to buy a high-quality bank that they can hold in their portfolio and not worry too much about, the hands-down pick is Wells over Citi.

You want clear direction Corporate identity crises aren't quite the same as the personal crises that might lead a 45-year-old guy to suddenly buy a bright red sports car. But since they can lead to a company making rash acquisitions, hasty divestitures, or boondoggles into new business lines, they can be just as damaging.

In the wake of the financial crisis, I believe fellow big bank Bank of America Corp (NYSE:BAC) is on a pretty straightforward path forward. Its increasing touchpoints with customers and abandoning business lines on the fringes that don't build customer relationships. Broadly speaking, it's building an integrated business organized around a core bank.

There are hints of Citigroup wanting to do something similar. Certainly, appointing Mike Corbat as the bank's new CEO appears to be a step in that direction. However, I think the overall -- dare I say "story" -- at Citi is not as clear as it is at other banks.