So when people are doing comparisons, do you use のほうが colloquially or even in text? I've seen AとBとどちらのほうが速いですか？ and also AとBとどちらが速いですか？
And the answers be:
But I wonder if normal colloquial Japanese wouldn't just express it as: Aが速いです。 or even Aはもっと速いです。 Can のほうが be left out when replying?
Yes, absolutely! One year in Japan and during that time I heard them using these kinds of sentence all the time. So, yes, it is a common issue.
I will provide a broader view for your question. You are actually asking about the following pattern:
(Noun)のほう(...)
Whose meaning is the one of pointing out something whenever two options are considered.
So, just start from the fact that ほう is put after a noun (using particle の) in order to say: This one is better. Or to indicate that the noun modified by ほう is the better choice.
When a question is giving you two options, generally it is necessary to express a preference. So the question can be:
1) (Noun-A)と(Noun-B)と、どちらが速いですか。 => Between (Noun-A) and (Noun-B), which one is fast?
2) (Noun-A)と(Noun-B)と、どちらのほうが速いですか。 => Between (Noun-A) and (Noun-B), which is the fastest?
3) (Group)で、どれが速いですか。 => In (Group), which is fast?
4) (Group)で、どれのほうが速いですか。 => In (Group), which is the fastest?
Possible answers can be (respectively):
1) (Noun-A)が速いです。 => (Noun-A) is fast！
2) (Noun-A)のほうが速いです。 => (Noun-A) is the fastest!
3) (Group)で、(Noun)が速いです。 => In (Group), (Noun ) is fast!
4) (Group)で、(Noun)ほうが速いです。 => In (Group), (noun) is the fastest!
As you can see, there are always two options! In the first two Qs and As it is obvious, but also when a group is involved there are two options. Consider the following example:
あの学{が}校{っこう}の先{せん}生{せい}の中{なか}で、だれのほうが優{やさ}しいですか。 => Among the teachers in that school, who is the nicest one?
In this case there are many teachers, but you are asking to consider only one and the rest, this makes two options out of many more!
Sentences 1 and 3 (both Q and A), you see that I did not use のほう. In such case you are not pointing out the best, the most appropriate, so you are just asking for the one that is fast, that's it. You are not stressing on the fact that you need, among all, the fastest! It is an important difference. In Q and A 1 and 3 you simply want a fast one, anyone can do! But in Q and A 2 and 4 you are asking for one particular, the fastest. It is a matter of stressing on your needs!
一{いち}番{ばん} is used, on the other hand, when more options are involved. This will let you understand when using のほう and when something else. So, as I said, many options. Consider the following questions:
1a) (Noun-A)と(Noun-B)と(Noun-C)と、どれが一{いち}番{ばん}いいですか。 => Among (Noun-A), (Noun-B) and (Noun-C), which one is the best?
The answer:
1a) (Noun-A)が、一{いち}番{ばん}いいです。 => (Noun-A) is the best!
As you can see, when you have many options, you use 一{いち}番{ばん}. But also in this case, you can use のほう. The previous example can be translated like this:
1a) (Noun-A)と(Noun-B)と(Noun-C)と、どれのほうがいいですか。 => Among (Noun-A), (Noun-B) and (Noun-C), which one is the best?
The answer:
1a) (Noun-A)のほうがいいです。 => (Noun-A) is the best!
The general rule is that when you have two options, you use のほう, while, when you have more options, you use 一{いち}番{ばん}.
However, in the context of many options being involved, if you wish to remark that one option in particular the most appropriate one, you can use のほう.
Be careful! You cannot use 一{いち}番{ばん} when two options are involved!
Final tip: when comparison is involved you have より. In these cases you use のほう.
Since I used patterns a lot, here are some examples:
Formal language:
吉野さん (Yoshino-san) >> この本とそれと、どちらのほうが安いですか。
吉川さん (Yoshikawa-san) >> あの、この本のほうが安いと思いますよ。
吉野さん (Yoshino-san) >> ごめんね、ちょっとペンを貸してもらえませんか。
吉川さん (Yoshikawa-san) >> ん！もちろん、どちらのほうが好きですか。
吉野さん (Yoshino-san) >> えと、右のほうが好きですよ。ありがとうね。
Plain style:
エミちゃん (Emi-chan) >> ねぇ、宿題が難しかったんだよ、困っちゃったぜ〜。
ケンちゃん (Ken-chan) >> ええ、そんなに難しくなかったぞ、やっぱエミちゃんは何も出来ねぇ。
エミちゃん (Emi-chan) >> ひどいよケンちゃん！１ページのほうが難しかったよ。ケンは出来た？
ケンちゃん (Ken-chan) >> えと、それだけ出来なかったんだ〜
エミちゃん (Emi-chan) >> ほら！！！何も出来ないのはどっちのほうだ？
ケンちゃん (Ken-chan) >> 分かった、分かったよ！ごめん！
Yes it is used all the time. Perhaps the best tip is that if you don't want to directly express your preferance ("I want") or direct tell somebody that they are wrong or something else is better you can make a more gentle suggestion using this expression.
I will just add some information on this phrase, as I think the other answers are adequate for your question.
のほう。。。is also used just to express preference or likes, without much of an emphasis on comparative meaning.
See for example, at 0:38 of this video, how this girl answers a question on where she lives:
http://www.youtube.com/watch?v=EJ8f5JwLkwM&feature=plcp
のほう。。or ほうが。。。is a very common phrase also used to express when one "should do something"=
家へ帰ったほうがいいよ
We better go home.
And in the example in your question, one could even answer the question " AとBとどちらが速いですか？ " with the brusque reply, " Aのほう。" (this would be an extremely colloquial and informal response.)
