Sell-side analysts believe Westpac stock has been over-sold in response to the bank's disappointing December quarter performance. Reports from JP Morgan, UBS and Macquarie Securities all argue Westpac will not repeat this performance and is now cheap relative to its peers. They all rate the stock a Buy.During February, ANZ led the banks, beating the market index, the S&P/ASX 300, by 2.5 per cent. Westpac lagged the market by 1.2 per cent. According to JP Morgan: "Westpac's stock price underperformed [that of] its peers in 2011 as the market was sceptical about the company's ability to take the required cost out of the business in the current low growth environment."More recently, the extent of Westpac's underperformance has been significant.Westpac reported a $200 million decline in markets' income in the December 2011 quarter, which was a result of widening spreads in its liquids portfolio, adverse credit valuation adjustments and lower treasury income. JP Morgan said: "Current market conditions see a repeat of adverse credit value adjustments and lower treasury income as less likely."Its rating on Westpac has changed from neutral to overweight.UBS said Westpac was also marked down because of weak cost performance. There were productivity-related restructuring costs; additional employee expenses, relating to the re-branding of St George Bank as Bank of Melbourne in Victoria; and expensed IT costs.UBS said the market had a tendency to assume poor performance would continue, rather than "look through it".UBS rates Westpac a Buy, and ANZ, Commonwealth Bank and NAB all Neutral.Macquarie Securities rates ANZ and Westpac Outperform, and Commonwealth Bank and NAB as Neutral.Analysts are at odds over the likely share price performance of ANZ. While Macquarie rates it Outperform, JP Morgan has downgraded the stock from neutral to underweight. It said: "ANZ's strong management team, differentiated focus on Asia and ability to address costs have all contributed to a strong share price re-rating over recent months."In our view, ANZ's current share price sees it at risk of being 'over-loved' and it is now the most expensive major bank relative to our fair value framework."