I'm having trouble using these two to my higher ups. Which is more polite?
くださる means "to give" while いただく means "to receive". In auxiliary usage, you express gratitude by using the former when the doer is the subject, and the latter when you, the recipient is the subject.
- おしえてくださって、ありがとうございます。 I appreciate that you taught me.
- おしえていただいて、たすかりました。 I was helped with your advice.
Some people (not me) say that sentences with いただく are more comfortable.
While いただく means receive and くださる means give, they are both used somewhat interchangeably. There is a minor grammatical difference:
Both sentences mean something like 'I am thankful that Mr Tanaka told me', or 'Thank you very much for telling me, Mr Tanaka', but いただく takes に and くださる takes が. Now then, on to usage differences.
With いただく, you are implicitly performing the action; with くださる, the honoured subject is performing the action. It is thus that いただく is politer, because it is considered politer to remove focus on the honoured one. Thus, you might use くださる talking to your boss, who is in your in-group but requires honorifics, while you would say いただく talking to customers, who are not only part of your out-group but require honorifics. (A lot of people would use similar forms talking to strangers as well, but that's another matter.)