- Follow place in the kana tables: ha, he, wo
- Follow pronunciation: wa, e, o
- If we go with pronunciation should we still go with "wo" for the object particle?
I think that since people will be thinking of the particles themselves when tagging that the pronunciation should be used wa, e should be used. However, を, is actually pronounced "wo" so that should be used. having "particle-o" might not very clear as to which particle it is while "particle-wo" is pretty clear (though this could just be because i'm used to thinking of を as "wo".
I would say to go with "wa", "e", and "wo" as proposed by Mark.
I think any (sane :)) naming scheme is fine as long as we apply tag synonyms to ensure that the questions are categorized properly and consistently.