In general, X-ray crystallography gives reconstructions of significantly higher resolution than does electron cryo-microscopy. Then why don't scientists simply skip electron cryo-microscopy and go straight for X-ray crystallography? The reason is that it is not always possible to crystallize viruses necessary for X-ray crystallography.
In our lab, we have been able to crystallize Norwalk Virus suitable for atomic resolution structural analysis by X-ray crystallography.