Always cite the most authoritative series which has reported the case.
Here is commonly recognised order of authority, with the most authoritative at the top of the list:
The Law Reports (AC, QB, Ch, Fam)
Weekly Law Reports
All England Law Reports
Specialist law reports, for example Lloyds Law Reports, Industrial Cases Reports, Reports of Patent Cases, Criminal Appeal Reports
All journal and newspaper reports are summaries, so should only be cited if the decision is not available in a full text report.