The classic one is "should have" or "should've" to "should of" because when spoken, it really does sound similar. I don't know what the fuck people are learning in English classes these days though, or if they even still have them.

They sound exactly the same to me.

Wiktionary gives <should've> as /ˈʃʊdəv/, unstressed <have> as /(h)əv/ and unstressed <of> as /əv/.