NEW YORK ( MainStreet) — Pick the odd city out: Chicago; Winter Haven, Fla.; or Newport Beach, Calif. And know such a place is where you do not want to even think about buying a home today.

Listen to the bubble watchers at real estate tracking company Trulia, and that is an easy challenge. Newport Beach - all of Orange County, in fact - is the one to avoid because, per Trulia, current home prices exceed what fundamental values say they should be by 17%.

That leads the nation in terms of real estate froth.

Trulia insists science backs its fundamental values. In a blog post, it explained what they are rooted in: "We look at the price-to-income ratio, the price-to-rent ratio and prices relative to their long-term trends."

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Find a town where incomes are low and, necessarily, housing prices will be likewise. If rents are low, so must housing prices. If they aren't, something - worrisome - is out of sync. If housing prices suddenly are shooting up after decades of stagnation in the area, that, too, is a warning sign of a bubble.

But just because house prices are high does not mean the town is in a bubble, said Trulia chief economist Jed Kolko in a Mainstreet interview. Case in point: San Francisco, where you have to be a dotcomer even to think about buying real estate (website Zillow pegs the median price at $971,600). But, said Kolko, Trulia numbers show Baghdad by the Bay is only 6% frothier than its fundamental values indicate the prices should be. That SOMA condo with an asking price of $1 million probably is fundamentally worth $940,000.

That's no bubble.

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Single-digit variations from the fundamental values, explained Kolko, are not necessarily a sign of a dangerous bubble - but even taking them into account, only 24 of the top 100 U.S. home markets look frothy, per Trulia's calculus. Of those, many are only very slightly overvalued (Dallas, Tex. and Sacramento, Calif. at +1% for instance).

How many metros are dangerously overvalued? And exactly where are the best buys in today's real estate?

The Trulia numbers offer guideposts.

The most undervalued homes in the nation are in the rustbelt - the once industrial midwest - where Akron, Ohio tops the chart at 21% below fundamental value. Cleveland, too, is 21% below fundamental value. Detroit is -19% and Dayton, Ohio is -16%.

Yes, but you want somewhere you might want to live? Feast on this: Chicago is 14% below fundamental value. So is Winter Haven, Fla. So is Providence,R.I.