FullTextSearch - UNION individual indexes or concatenated columns index ?

I'm attempting to implement full-text search and am torn between two techniques:

1) Create multiple GIN indexes on columns I'm going to search against and UNION the results
or
2) Create one concatenated column GIN index consisting of the columns that will be searched.

Is there any performance considerations that may make one technique better than the other?

Thanks for insight,
Jer

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