Which one, and which is the most?

To compare two choices, use A と B と どちら が + adjective + です か. コーヒー と お茶ちゃ と どちら が 好すき です か asks “Which do you prefer, coffee or tea?”

一番いちばん means “number one” and can mark a superlative before an adjective. 一番いちばん 大おおきい means “the biggest.” The Japanese adjective stays in its normal form; English may need “-est” or “most.”

Use 〜の 中なか で to name the group you are comparing within. 犬いぬ の 中なか で これ が 一番いちばん 大おおきい です means “Of the dogs, this one is the biggest.”

In these identifying patterns, が marks the choice being singled out. Learn that structure without treating it as a ban on は in every possible comparative sentence. The comparison group may be stated explicitly or understood from context.