Great question, Irene.

I'm going to partially disagree with Shachi.

I base this on my life as a native English speaker, having lived for forty years in four "inner-circle English" countries on three continents.

As you can imagine, this builds up quite an internal linguistic database regarding English!

While both do mean essentially the same and both are entirely correct, both for speaking and for writing, the first implies more strongly that B is particularly cheap. In speaking, with the necessary emphasis, that meaning would be even more strongly evident.

Irene, I hope you never lose your curiosity to ask such relatively subtle questions!

This interest will surely take you to a high level in English.

The second sentence is better to use.

Mo Reddiford , thank you very much , I even couldn't imagine that "my choice" depended on "power" of difference between subjects. I like such answers like yours , they help me to realize language. Thank you!:)

Thank you))

as...as: you can use for positive sentence and negative sentence.

so...as: you only use for negative sentence.

Therefore, they are the same when you make a negative sentence.