The Share Centre has rated Astrazeneca a 'hold' for medium-risk investors after fourth-quarter results from the drugmaker disappointed the market on Thursday, with the broker highlighting its preference for sector rival Glaxosmithkline (GSK).The company reported a 2% increase in revenues to $6.68bn for the last three months of 2014, missing analysts' estimates slightly. However, earnings per share slumped by 28% to 76 cents due to an increased focus on research and development (R&D) and higher marketing costs."The company is in a transition phase investing heavily into R&D to boost its drugs pipeline with the hope of mitigating falling sales caused by generic competition," said analyst Helal Miah from The Share Centre."While the increase is promising, this does not guarantee that sales will eventually turnaround and we believe that more evidence of progress is needed. Investors should be aware that even if there is development, it will still be some years before there is a material impact on sales growth."The analyst still reckons that Astrazeneca will "continue to pay a good dividend and we wouldn't discourage investors attracted by the strong income flows"."However, investors should take note that the current price-to-earnings ratio of 17x leads us to prefer GSK, which trades at lower multiples. We expect to see results much sooner from GSK, courtesy of investment in R&D being made much earlier," Miah said.Astrazeneca was trading down 1.9% on Thursday morning while GSK rose 1.7%, extending gains made on Wednesday after its own results impressed.