Currently, there is currently a proposal to make estimation a synonym of estimating. However, I think this is backwards: if the choice is only between these two words, then estimation should be the canonical tag and estimating should be the synonym.
While it's true that estimating has more tagged questions, I think that's an historical artifact. In addition, most of our tags are nouns or gerunds, whereas estimating is a verb.
However, we have other options that might be even better. For consistency, and based on the Google Ngram of the related word forms, I'd really like to see estimates become the canonical link rather than the other two.