Install 2nd wordpress site in subdirectory or subdomain

Hi wordpress community!

I have a quick question for you: i have a site running at https://www.ambassdorbase.at and i want to install a 2nd wordpress site either on ambassadorbase.at/2ndsite oder 2ndsite.ambassadorbase.at

what are the pros/cons of doing it on a subdomain or on a subdirectory?

The site will only run for a few weeks, its a campaign which will go offline. So the SEO/google part can be ignored here.

thank you!

rolf