present perfect tense

[acrunway]

I quote following from other webiste,

Please note that it’s clearest to avoid contractions when using the present perfect tense with the negative, at least in American English.

I’ve not seen the Eiffel Tower. incorrect

I have not seen the Eiffel Tower. correct

would anyone please enlighten this further, in daily use, somehow I heard both way,

are there any difference between I have not vs I haven't ?

I have not seen the Eiffel Tower, vs I haven't seen the Eiffel Tower

thanks in advance

[Alan]

I have not (seen): written/formal usage

I haven't (seen): standard conversational contraction

I've not (seen): nonstandard (mainly Northern English dialectal) usage