It's hard to select an adjective because they all more or less overlap. About the familier requirement, none of them are particularly colloquial but they are all well known by everyone.
The choice also depend on what characteristic you want to focus on.
I would anyway go for:
C'est un étudiant/employé très méticuleux.
Minutieux would be a close second, the person is also doing their homework accurately, the opposite of botching.
A person consciencieuse is focused about ethics.
Scrupuleux is like consciencieux, but more negative, the work might not actually be done for fear of breaking a rule.
Reyedy suggested rigoureux which belongs indeed to the same set. Here the focus is on the care with which the rules are followed, even though it might be painful. According to Google books, rigoureux is three to six times more popular in printed material that the remaining adjectives of the list: