Why not have both? SE has this handy feature called tag synonyms, which, as far as I understand, will automatically remap a shorter tag that's easier to type to its longer, "canonical" version. So we should simply decide for each group of clearly synonymous tags which should be the "main" one and mark all the others as synonyms of the first.
The only problem with that at the moment is that one has to have no less than 1250 rep on the site (and 5 tag reputation) to merely be able to suggest a tag synonym, and we have very few such users at the moment.
A possible workaround for the time being could be to create a thread, either in DSE.Meta or in chat, where anyone can propose merges verbally and then those with the privilege could do the actual synonymizing.
As for which should be the master tag, I'd vote for the longer version. That would make the tags easily understandable by anyone reading the question, while keeping the option to type the short version.