NEW YORK ( TheStreet) -- Only five actively traded insurance stocks are currently assigned coveted A+ (Excellent) ratings by TheStreet Ratings, and all are property and casualty carriers. TheStreet Ratings takes a very conservative approach to rating all stocks publicly traded on the New York Stock Exchange, AMEX and NASDAQ, that have at least five quarters of financial data available. The ratings emphasize long-term total returns, as well as revenue trends, capital strength and dividends, while also considering short-term performance, financial stability and volatility. A rating of B-minus (Good) or higher is considered a "Buy" recommendation. It's been a difficult two years for many insurance companies in the prolonged low rate environment. Property and casualty carriers are "particularly sensitive to low interest rates," according to Gavin Magor, a senior analyst with Weiss Ratings, since the group "typically seeks to break even on underwriting premiums, while making profits on cash invested in securities." The P&C carriers are "still under significant pressure and are struggling to implement a normal pricing that you would see in a hard market, due to oversupply." Magor does see opportunities among certain P&C carriers that may be undervalued, saying that "speculators may start to look at the surviving bond and mortgage guaranty insurers, but they are not for Granny's pension." Life insurance companies are also under pressure, as "profitability for the largest ones dropped by 84% during 2011," according to Magor, because "the life insurers have had a lot of guarantees on their annuities that they have to live up to, while they haven't got the yields to back them up." Insurers have underperformed banks so far this year. The KBW Bank Index ( I:BKX) was up 10% year-to-date, through Wednesday's close at 43.42, while the KBW Insurance Index ( I:KIX) was down 1% to 109.50. A quick look at two of the largest U.S. insurance companies -- by market capitalization -- paints a stark contrast for share valuations, and a possible opportunity for investors. The shares closed at $81.72 Thursday, returning 7% year-to-date, following a 5% return during 2011. The shares trade for 1.8 times tangible book value, according to Worldscope data provided by Thomson Reuters, and 15 times the consensus 2013 earnings estimate of $5.40 a share, among analysts polled by Thomson Reuters. The consensus 2012 EPS estimate is $4.93. Of course, being led by the legendary Warren Buffett supports quite a premium for the shares. TheStreet Ratings rates Berkshire's class B shares A-minus. MetLife ( MET) is rated C+ by TheStreet Ratings. The company's shares closed at $29.17 Thursday, down 6% year to date, after declining 28% during 2011. The shares trade for 1.1 times tangible book value and just five times the consensus 2013 EPS estimate of $5.63. The consensus 2012 EPS estimate is $5.22. MetLife is in the midst of a transition from being considered a bank holding company, and hopefully escaping regulatory supervision by the Federal Reserve. The company agreed in November to sell "most of the depository business" of its MetLife Bank subsidiary to General Electric ( GE) (GE) unit GE Capital. In January, MetLife announced it was exiting the forward residential mortgage business. The company continues to originate reverse mortgages and to service existing mortgage loans. During March, MetLife's plan to increase its return of capital to investors during 2012 was rejected by the Federal Reserve. The sale of the MetLife Bank depository business is expected to be completed before the end of the second quarter, after which the company plans to deregister as a bank holding company. Out of 21 sell-side analysts covering MetLife, 18 rate the shares a buy. With such a low multiple to forward earnings, patient investors willing to wait for the company's transition and for the eventual return of capital, may be looking at quite a bargain. Meanwhile, the shares have a yield of 2.54%, based on 74-cent annual dividend, paid in November. The insurers rated A+ by TheStreet Ratings trade at valuations to forward earnings between those of Berkshire Hathaway and MetLife. Here they are, in order of descending valuation to consensus 2013 earnings estimates.