Barclays is the top pick in the UK banking sector, according to Nomura, which retained its 'buy' rating for the stock on Tuesday morning.The broker also kept a positive stance on Standard Chartered, but downgraded its rating for HSBC and reiterated its negative position on RBS. Lloyds, meanwhile, looks fairly valued, it said.Barclays was upgraded to 'buy' by Nomura back in September prior to its £5.8bn rights issue and the broker has stuck with the bank as its sector preference, saying that the valuation looks "attractive"."We believe the expected deleveraging plan will lead to higher capital ratios and structurally higher returns on tangible equity (ROTE), which should drive a re-rating," said analyst Chintan Joshi.As for StanChart ('buy'), Joshi said after a "difficult 2013" - on the back of margin contraction and expectations of lower Asian growth - the stock is now trading at a "negative growth multiple". "We think a lot of negatives are priced in, and if STAN can achieve current consensus expectations, it could re-rate through 2014".The analyst said that regulation - admittedly a risk for all UK banks - is a headwind to the dividend story at HSBC. "Therefore [we] downgrade the name to 'neutral' until there is further visibility, despite still expecting some upside in the name".RBS is labelled as the broker's least preferred bank in the UK and downside is expected from current levels. "A slow normalisation to double-digit ROTE, litigation risk and political influence remain the key reason for our 'reduce' rating."Upside at Lloyds (rated 'neutral') looks "limited against high current expectations and valuations".BC