I don't really know which one should be preferred.
This is a good spot for tag synonyms because the spellings are so different.
Without tag synonyms, I would favour going with
Honestly there really isn't a good solution to picking one or the other without the synonyms.
EDIT: Now that tag synonyms have been implemented, there is a synonym in the system mapping
I would always prefer the full version unless the initialism/abbreviation is so thoroughly ubiquitous that the original is rarely-to-never used (think IBM != International Business Machines).
This is a good candidate for tag synonyms.