A is more (property) than B.
A のほうが Bより(property).
Between A and B, which is more (property)?
A とBと どっちのほうが (property)。
Which is cheaper, going by bus or by train?
バスと電車とどっちのほうが安いですか。
A is a better singer than B.
A のほうがBより歌が上手(じょうず)です。
Between A, B, and C, who do you think is the best singer?
AとBとCの中で、誰が一番歌が上手だと思いますか。もちろん、Aが一番歌が上手です。
Alternates for どっちのほう - どちらのほう、どっち、どちら. どっち、どっちのほう are slightly more colloquial than the other two.
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When a noun follows an adjective, and when it is clear what you are referring to, you can replace the noun with の.
I have a black sweater. I have a red one, too.
黒いセーターを持っています。赤いのも持っています。
I went to buy an inexpensive dictionary, but there were no good ones.
安い辞書を買いに行きました。でもいいのがありませんでした。
American ice cream is more delicious than Japanese one.
アメリカのアイスクリームのほうが日本のより美味しいです。
のほうand どっちare not used in statements of comparison among three or more items. Normal question words like だれ、どれ、and何 are used instead.
The tendency is to use どれ when a list of items is present, and to use なに when a group is referred to collectively.
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Which do you like the best, apples, tangerines, or cherries?
苹果とみかんとさくらんぼの中で、どれが一番好きですか。