I couldn't help laughing at the silly joke

Dear native English speakers,
Would the pattern "couldn't help (do)ing" be commonly used in modern English?
I have an impression that Americans prefer to use the pattern "couldn't help but (do)".

How about these? Would all of them sound natural?
(1a) I couldn't help laughing at the silly joke. [This is from our textbook.]
(1b) I couldn't help but laugh at the silly joke.
(2a) I couldn't help thinking that he had known this fact.
(2b) I couldn't help but think that he had known this fact.
(3a) I couldn't help crying when I heard his sad story.
(3b) I couldn't help but cry when I heard his sad story.

Thanks in advance.
Hirashin

I would say the sentences for both (1) and (2) sound natural to me. I think switching the word order up on the last two sentences would sound more natural. "When I have heard his sad story, I couldn't help but cry." "When I heard his sad story, I couldn't help crying." Although other wording might sound more natural, "When I heard his sad story, I couldn't not cry/stop crying."

It's reasonably common in writing, though I'd say less so in speech. That goes for both of them. I don't see a major distinction between the two styles.

The gerund is a little more common than the but form, but also very common: I couldn't help myself (alluding to something you've already done)

Thanks for the help, Julimaruchan and nahadef.