TSC Ratings provides exclusive stock, ETF and mutual fund ratings and commentary based on award-winning, proprietary tools. Its "safety first" approach to investing aims to reduce risk while seeking solid outperformance on a total return basis.TheStreet.com Ratings' model downgraded Blackstone Group ( BX) to "sell." The private-equity firm offers funds that invest in companies, real estate and hedge funds. The numbers: First-quarter revenue fell 31% from a year earlier to $47 million as the company swung to a net loss of $231 million or 84 cents per share. Margins remained negative, but Blackstone's net loss declined from the fourth quarter. The cash balance improved 6.7% over last year's first quarter and the company reduced its debt burden 95% to $83 million. The stock: Blackstone is up 34% this year after falling 70% in 2008. The stock offers a huge 13.7% dividend yield and management is confident about its ability to achieve a full payout in 2009. The model downgraded BOK Financial ( BOKF) to "hold." The company provides money management and banking services. The numbers: First-quarter revenue fell 9.7% to $358 million as net income and earnings per share declined 12% to $55 million and 81 cents, respectively. Operating margin improved 194 basis points to 36% and net margin fell 35 basis points to 15%. The company has $715 million of cash reserves, but a hefty $4.9 billion debt burden. The stock: BOK Financial shares are down 12% this year, underperforming the Dow Jones Industrial Average and the S&P 500 Index. The stock has a price-to-earnings ratio of 16 and offers a 2.7% dividend yield. The model upgraded Harbin Electric ( HRBN) to "buy." The company designs and produces electric motors in countries including China. The numbers: First-quarter revenue climbed 37% to $30 million as net income increased 62% to $8.7 million and earnings per share improved 44% to 39 cents. Its operating margin shrank 12 percentage points to 26% and net margin declined 4 percentage points to 24%. The company has a low debt-to-equity ratio of 0.21 and a high quick ratio of 4.23, indicating ample liquidity.