Tough call, eh? :-)
Given a DOI, CrossRef's OpenURL won't give you any author except the first author, and won't give you the end page of an article. In other words, it won't give you enough information to create a citation for a paper.
And PubMed? PubMed will give you all the authors, though it truncates them all to two initials. If you want the full journal name, you will have to capitalise it yourself, which isn't trivial to do automatically (e.g. "Journal of the american chemical society"); if you want the journal abbreviation, you will have to insert the periods yourself, which again isn't quite trivial (it's not just a question of sticking a period in front of everything in sight).
My favourite thing of all about PubMed is that even where a paper is in PubMed and where the paper has a DOI, the DOI mightn't be in PubMed (e.g. doi://10.1016/j.jmb.2003.08.006 and PMID 14499606). Nice. This last one means that to get PubMed metadata relating to that DOI, you need to first look up CrossRef, and then use that metadata (i.e. journal, year, volume and startpage) to look up PubMed.
So, which do I think is worse? CrossRef - but only because it doesn't give enough information to create a citation.