Cleft sentence

The right one would be Its me who is going to do it.

Both are right.
I just want to know which one is used more often in conversation.

In conversation you would say "I am going to do it"

Thanks,

Yes, I guess you just stress the element you want to emphasize,
but don't you ever use any of the sentences above?

tarirotariWhich one do you use when speaking?

Neither. I wouldn't use either of those in a million years!

Here's what I say:

I'm the one that's going to do it.

CJ

Yes if you want to emphasize then I agree with CJ.

So would it sound a bit weird to you if somebody used any of those sentences? Would it perhaps sound a bit pretentious or pompous, or...?

And what about cleft sentences emphasizing other elements:

It's on Wednesday that we must visit him.
No, no. It's the big steak that you must put on!

Are they also hardly used in spoken English? Would it be weird to

It's on Wednesday that we must visit him.

No, no. It's the big steak that you must put on! ...

Those would sound quite unnatural, but I can imagine saying "It's me who's got to do it."

tarirotariSo would it sound a bit weird to you if somebody used any of those sentences? Would it perhaps sound a bit pretentious or pompous, or...?

Pretentious. Pompous. Strange. Yes. Any of those. (To my ear.)

tarirotariAnd what about cleft sentences emphasizing other elements:

It's on Wednesday that we must visit him.

Thank you all guys,

I knew this kind of structures were not common in speech but, quite frankly, I didn't expect they were so rarely used.

But now that I get to think about it, they might even be uncommon in writing, where the use of italics for emphasis is also quite extended.

Thank you all again