at any rate; in any case; either way
Used to introduce a conclusion or statement that holds regardless of the preceding circumstances. Often appears at the beginning of a sentence.
At any rate, we have to decide by tomorrow.
I don't know if he'll come, but either way, let's get ready.
いずれにせよ is a more formal, logical way to say 'either way, be that as it may', whereas ともかく is casual and conversational.
いずれにせよ is a formal, neutral way to say 'in any case', lacking the emotional resignation or scorn that どうせ often carries.
いずれにせよ is a slightly more formal, written variant of いずれにしても with the same meaning of 'in any case'.
Derived from いずれ (which, whichever) + に + せよ (imperative form of する, 'do'). Literally 'whichever it may be'.