Investec has turned more bullish on global banking giant HSBC, upgrading the stock from 'add' to 'buy', but has retained a clear preference for sector peer Standard Chartered (also rated 'buy').Analyst Ian Gordon said in a research note on Friday that both HSBC and StanChart are expected to deliver further outperformance against UK domestic lenders Lloyds and RBS (both rated 'hold')."[...] but in the case of HSBC, a continuing inability to deploy its emerging capital surplus will, we believe, lead inevitably to suboptimal (below target) returns. Most investors do candidly acknowledge this reality already, which rather begs the question.....why own HSBC at all?"Gordon highlights that HSBC remains the perennial "'generalists' favourite bank" given its dividend-paying capacity. However, management has demanded a couple of years to explore opportunities for growth before starting to think about returning capital, and as HSBC's sharecount increased by 3.4% last year, Gordon thinks that this suggests that capital flows are currently moving "in the wrong direction". Meanwhile, he said that weak loan growth, declining net interest margin and lower revenue growth within the Global Banking & Markets division are "key headwinds".Barclays ('buy') remains Investec's top pick in the sector overall.Gordon said: "On 0.8 times tangible net asset value with a clear, cost-led recovery path to a 10.5% return on equity in 2015e, despite an extended period of outperformance, we continue to see [Barclays'] valuation support as compelling."