いずれにしても

Meanings

usually written using kana alone

Used to introduce a conclusion or decision that holds regardless of the circumstances; similar to 'anyway' or 'at any rate'.

いずれにしても、〈事こと〉は変かわらないEither way, 〈thing〉 doesn't change
いずれにしても、結けっ果かは変かわらない。
Either way, the result won't change.
いずれにしても〈動どう詞し〉なければならないIn any case, one must do 〈verb〉
いずれにしても、明日あしたまでに決きめなければならない。
In any case, we have to decide by tomorrow.

とにかくN3
とにかく is a casual way to push past obstacles and get to the point, while いずれにしても is more neutral and simply states that the conclusion holds regardless of circumstances.
どっちにしても
どっちにしても is the colloquial spoken equivalent of いずれにしても, used in casual conversation rather than writing.
いずれにせよ
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'.
どの道みち
どのみち stresses that an outcome is unavoidable no matter what path is taken, whereas いずれにしても simply notes that a conclusion is the same regardless of the situation.
ともあれ
いずれにしても stresses that the conclusion holds regardless of various possibilities, whereas ともあれ simply sets aside what was just said to move on to the main point.

Derived from いずれ (which, whichever) + にしても (even if it is). The kanji 何れ is the standard but rare spelling for いずれ; 孰れ is an archaic variant.