Elife is backed by the largest non-profit funding medical research in the United Kingdom (the Wellcome Trust). Its editor won a Nobel Prize recently. I know these are somewhat shallow proxies for trustworthiness, but good enough for me ;)

(As for the more general question - how do you decide this in general, in a field you're new to - I don't know. Probably asking in a thread on HN is a very good strategy actually :))