The number of subpages on your domain determines what premium subscription is set per domain. You do not need to make an active choice, since the correct subscription will be determined by the Cookiebot scanner based on the number of subpages:
If the scanner finds less than 500 pages -> Premium Small
If the scanner finds less than 5000 pages -> Premium Medium
If the scanner finds more than 5000 pages -> Premium Large
Please note that you will need a subscription for each of your domains and subdomains. See also: Do subdomains require a seperate subscription?
You can add an unlimited amount of domains to your Cookiebot account and each domain will be set as a Small, Medium or Large subscription.