The "Ask Question" form currently suggests tags in the placeholder text: grammar, word-choice, etymology. I would guess that these are the most common tags used.
However, are they the most useful examples to offer? I think we should probably offer tags which are likely to produce the most improvement in a question. The questions with the greatest likelihood for improvement are (I think) those whose authors should read the help available on single-word-requests and prepositions. Perhaps we could also offer tenses.
I certainly don't think that grammar or grammaticality should be offered at all.
If we had the opportunity to change this helper text, what tags would you like to see here? Please add one per answer, and upvote/downvote according to how suitable for question askers you feel the suggestion would be. [Suggesting a tag in an answer should be assessed as a single upvote by the author.]
Note that you can get a tag to appear in an answer and be clickable by using the syntax
[tag:etymology] to get etymology.