Ahead of earnings season in the mining sector, Credit Suisse has labelled its top and worst picks among resource stocks."Our top picks are Rio Tinto and ENRC and from the mid cap group African Minerals and London Mining."While Lonmin is downgraded from 'outperform' to 'neutral', the broker's least-preferred stocks are Anglo American, Kazakhmys and Antofagasta.UBS has hiked its target price for engineering giant Weir by 15 per cent from 2,000p to 2,300p and reiterated its 'buy' rating for the stock, causing shares to rise on Friday morning.The broker highlighted results from Weir's peer group, specifically Metso and Outotec, which surprised on both orders and profits on Thursday.Investec has reduced its rating for tobacco and cigarette giant Imperial to 'hold' and cut its target price from 2,580p to 2,450p, saying the first quarter was the signal to prompt the abandonment of its 'buy' case."The Q1 felt like a signal event to us. Sales were barely ahead against a weak comp and profit is set to be lower in H1, as tough conditions in Europe and elsewhere press on IMT's organic growth aspirations," said analyst Martin Deboo.BC