I would do it using ContentArea('ID') AMPScript function:

Build 7 separate content areas, containing HTML for the hero of the email, and select each of them, based on the weekday.

SET @today = Format(SystemDateToLocalDate(Now()), "dddd")

Then build IF / ELSE IF which switches between the different content areas, based on the value of @today

I would do it using ContentArea('ID') AMPScript function:

Build 7 separate content areas, containing HTML for the hero of the email, and select each of them, based on the weekday.

SET @today = Format(SystemDateToLocalDate(Now()), "dddd")

Then build IF / ELSE IF which switches between the different content areas, based on the value of @today

EDIT:

You might not even need to use a DE to map dates and content IDs. Imagine this scenario. You add a number field to your sendable DE, which you increment for each email sendout. This field is then read into the email, into the @JourneyDay - then you can use it to retrieve the content areas, named: Day1, Day2, Day3 and so on.

%%=ContentBlockByName(Concat("Content Builder\Day",@JourneyDay))=%%

I would do it using ContentArea('ID') ampscript function: https://developer.salesforce.com/docs/atlas.en-us.noversion.mc-programmatic-content.meta/mc-programmatic-content/contentarea.htm

Build 7 separate content areas, containing HTML for the hero of the email, and select each of them, based on the weekday. SET @today = Format(SystemDateToLocalDate(Now()), "dddd")

Then build IF / ELSE IF which switches between the different content areas, based on the value of @today

I would do it using ContentArea('ID') AMPScript function:

Build 7 separate content areas, containing HTML for the hero of the email, and select each of them, based on the weekday.

SET @today = Format(SystemDateToLocalDate(Now()), "dddd")

Then build IF / ELSE IF which switches between the different content areas, based on the value of @today