を問(と)わずRegardless of, Whether or not, No matter, With or without

Both mean regardless of, but differ slightly in register. にかかわらず is more formal or literary, often used even with negative implications, as in 年齢にかかわらず (Regardless of age). を問わず is more common in daily usage, treating conditions equally without preference, as in 学歴を問わず (Regardless of academic background).

Both can mean regardless of, but are used differently. にもかかわらず expresses a surprising or unexpected result in spite of circumstances, as in 年齢にもかかわらず元気だ (In spite of his age, he is energetic). を問わず applies more broadly and neutrally, indicating that something holds true in all cases, as in 性別を問わず参加できる (Participation is open regardless of gender).

を問わず follows a noun (often a category) to show disregard for distinctions, as in 年齢を問わず (Regardless of age). にせよ・にしろ also implies that something holds true under different conditions, but it typically introduces a possibility that is then contrasted or disputed, as in 行くにせよ行かないにせよ (Whether you go or not…). を問わず highlights inclusiveness, while にせよ・にしろ highlights hypothetical contrasts.

～ても～なくても and を問わず both express 'regardless of', but ～ても～なくても contrasts doing something with not doing it, e.g. 雨が降っても降らなくても ('whether it rains or not'), while を問わず states that something holds true regardless of category or attribute, e.g. 年齢を問わず ('regardless of age').

どうしても and を問わず share the meaning of 'no matter' or 'regardless of', but are used differently. どうしても appears at the beginning of a sentence to express persistence or inevitability. For example, どうしても勝ちたい ('I want to win no matter what'). を問わず usually follows nouns or question words and shows that something holds true regardless of conditions. For example, 年齢を問わず参加できます ('You can participate regardless of age').