TheStreet.com 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 outperformance on a total return basis.TheStreet.com's stock-rating model upgraded America's Car-Mart ( CRMT) to "buy." The company sells used cars in the U.S. The numbers: Fiscal fourth-quarter revenue rose 2% to $72 million from a year earlier. Net income fell 15% to $5.1 million and earnings per share dropped 16% to 43 cents as net margin slipped from 8.6% to 7.1%. The company has a weak cash balance with just $100,000 of reserves, but a debt-to-equity ratio of 0.2 demonstrates modest leverage. The company is benefitting as budget-conscious consumers buy used cars The stock: America's Car-Mart is up 47% this year, outperforming major U.S. indexes. The stock trades at a fair price-to-earnings ratio of 13 and doesn't pay dividends. The model upgraded specialty insurer Allied World Assurance Holdings ( AWH) to "buy." The numbers: First-quarter revenue increased 12% to $397 million as net income and earnings per share inched up to $131 million and $2.57, respectively. Operating margin fell from 40% to 39% and net margin dropped from 37% to 33%. Although the cash balance has fallen 44% from a year earlier, it's still ample with $704 million in reserves. And the debt-to-equity ratio is low at 0.2. The stock: Allied World Assurance has increased 2% this year, outperforming the 3.6% decline of the Dow Jones Industrial Average and 1.6% gain of the S&P 500 Index. The stock trades at a low price-to-earnings ratio of 12, but offers a weak 1.7% dividend yield. The model downgraded Cowen Group ( COWN), an investment bank that provides research and trading services, to "sell." The numbers: First-quarter revenue fell 21% to $44 million as the company swung to a net loss of $6.5 million or 57 cents per share. Operating margin fell deeper into negative territory as strategic advisory revenue dropped 72% from a year earlier and 34% from the previous quarter. The company has a strong financial position, with $86 million of cash and just $27 million of debt, but will likely face more obstacles this year. The stock: Cowen is up 17% this year, outperforming the Dow and S&P 500. The stock doesn't pay dividends.