OISD FULL

Mark On Scale having custom filters can work but would probably increase prices as it requires every single custom list to be cached or to have downtime copying the said list, as people would put custom lists, modifications of current lists and generally so many variants  that it wouldn't be too logical. Adguard as the App or the Home runs locally so the only person adding / deleting and making sure the hardware works out is you when you x that by let's say 5,000 users it starts becoming iffy, 50,000 users then the servers need a lot of upgrading that would show up in terms of price changing in the users bill.

As a side note, the OISD that NextDNS uses is the Full filter, you can see this by going to the GitHub (https://github.com/nextdns/metadata/blob/master/privacy/blocklists/oisd.json)