Student or Learner
According to Macmilland dictionary, estimation is a formal word, but on the other hand it is not according to Cambridge dictionary.
Is estimation a formal word ?
estimation - definition of estimation by Macmillan Dictionary
estimation noun - definition in Learners Dictionary - Cambridge Dictionary Online
Esteem (Cambridge) is defined as formal as is in Macmillan. As a rule, I'd say if a word is not specifically labelled as "informal", it is safe to use it without it sounding awkward in formal texts. The fact that "estimation" is not defined specifically as "formal" by Cambridge does not make it informal, it just means that the editors of the dictionary do not consider it formal, but rather an "everyday English" word, IMO.
Please be aware that I'm neither a native English speaker nor a teacher.