it's not life that matters but the journey...

I need some grammar advice, once again. I know that I'm really supposed to be a grammar expert - or at least as a native English speaker I'm supposed to be the English "expert" when I'm teaching here in Japan. But sometimes I start to look at the English in these Japanese textbooks, and the English that the students are learning, and it seems wrong. Then I begin to second-guess myself, and I can't find the right answers online or in my books.

We've been teaching comparatives and superlatives - you know, I'm taller than my sister. My brother is the tallest in my family ... etc...
But one of the comparative/superlatives that confuses me is when we talk about things we like.
For example:
I like strawberries better than I like bananas.
or
I like strawberries better than bananas.

But how about this sentence:
I like strawberries more than I like bananas.

And what about the superlative version? Which is preferable, for you?

I like strawberries the best (of all fruits).
OR
I like strawberries the most (of all fruits).

when we ask the question, "Which fruit do you like (the most) (the best)?

Isn't it okay to use both "best" and "most" when we talk about our favorite things?

Because in this case, we're not using "best" to mean quality - as in "Sushi is the best Japanese food." And we're not using "most" to mean quantity - as in "I have more books than she does - I have the most books."

I think when we're talking about what we like, it is interchangeable to use "most" and "best" - but then again I am always doubting myself as an English grammarian!
So what do you think?

I sometimes wonder why I'm teaching English in Japan. Sometimes I really think that despite my 8 years of experience teaching English, and my MA in English, I still don't really know the English language well enough. so since I've searched and searched online and can't really find an answer, maybe someone out there can help me. can you?

I'm trying to figure out how to explain to one of the Japanese English teachers at the junior high school why this sentence: English is fun to learn.
is better than this sentence: To learn English is fun.

I know that you CAN use infinitives as subjects in a sentence, as in this example:
To climb Mt. Everest has always been my dream.

BUT to me it's more natural, or just better English, to say this:
It has always been my dream to climb Mt. Everest.

??

I think it depends on what you want your subject to be.

See, I gave the 9th graders a warm-up game the other day. They got into groups of five students, and each student was assigned a number, from 1-5. I took a five-word sentence and broke it up, putting each word on the board one at a time. Each "1" student would look up at the board when I wrote their word (word "1") and the others would "sleep." And so on, until each student had seen their own word. When each student had been given his/her word, they would come together as a group and put together the words into a sentence.
I gave them the following words: English, fun, learn, is, to
And they came up with the two versions above (as well as others which weren't correct at all).

So is it acceptable to say "To learn English is fun."?
I don't think it's grammatically incorrect, but at the same time I don't think that it's really good English.

English experts, please help me.

Thanks!