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If you invested in the 10 U.S. insurance stocks with the lowest price-to-book values during the past six weeks, you would have made a 61% return.

But fear not, you have not missed the boat. The top performers were

Radian Group

(RDN) - Get Report

, up 170%;

MGIC Investment

(MTG) - Get Report

, with a gain of 120%;

Conseco

(CNO) - Get Report

, up 83%; and

Hartford Financial Services

(HIG) - Get Report

, which rose 65%.

As most insurers have reported second-quarter results, it's time to review those that offer the best bargains. The criterion is book value -- how much you pay for the stock compared with the company's net asset value. Many past winners are still worth considering.

As insurers recover from the beating they took since last year, some insurers are still cheap.

PMI Group

( PMI) leads with a 19% price-to-book value. It was also on the June list with a 14% price-to-book, as the price has since risen 36%.

Any investment should be reviewed regularly -- at least quarterly -- if you're using book value as the benchmark. There are opportunities, and some risk, in investing in the stocks, but the rewards may be high. Mitigating risk by investing in all or a number of the shares might provide growth opportunities with lower risk.

The current top 10 stocks aren't for the faint-hearted and include one,

American International Group

(AIG) - Get Report

, that shouldn't be a part of a retirement plan. It has a current price-to-book value of 24%.

The balance of the top-five stocks for consideration consists of survivors from the prior quarter's top-10 list.

Phoenix

(PNX)

, at 23% of book value, still represents great value despite a 28% rise in the share price. Conseco, one of the biggest gainers in the past six weeks, has a current price-to-book value of 25%. Radian, which posted the biggest stock-price increase, is still worth a look. It has a price-to-book value of 27%.

Sometimes you can be surprised. Finding

Genworth Financial

(GNW) - Get Report

still in the top 10, with a price-to-book value of 38%, after a 39% gain in the share price demonstrates how hard insurers were hit in the past year. After tripling this year, Genworth is still 40% below where it was just 12 months ago.

Some insurers are a risk. Aside from AIG,

MBIA

(MBI) - Get Report

has problems that could be drawn out. To offset that risk, the price-to-book of 44% could be considered very attractive.

MGIC, the mortgage insurance guarantee company, has multiple problems, including concerns over regulatory capital requirements. It has delayed the launch of a new company that was planned to write new business starting in January. Despite that, the stock has risen, and the company has a low 49% price-to-book value.

The two others on the list are

Kingsway Financial Services

(KFS) - Get Report

and

First Acceptance

(FAC)

.

If you were wondering about The Hartford, which had a significant stock-price increase, it's no longer on the top 10 best book-value list. But with a 59% book-to-value, it could well reappear on the list if the third quarter ends up being as good as it started.

Gavin Magor joined TheStreet.com Ratings in 2008, and is the senior analyst responsible for assigning financial strength ratings to health insurers and supporting other health care-related consumer products, including Medicare supplement insurance, long-term care insurance and elder care information. He conducts industry analysis in these areas. He has more than 20 years' international experience in credit risk management, commercial lending and analysis, working in the U.K., Sweden, Mexico, Brazil and the U.S. He holds a master's degree in business administration from The Open University in the U.K.