I like what Isopod did, linking them directly to a instance.
The only way to catch the average joe is to hold their hand and get them to content as quickly as possible. While linking them to the largest instances may not be the healthiest for decentralization, it's going to give newcomers the best experience.
A lot of redditors, I'd even say the majority now-a-days, use the app. While a lot of the Lemmy apps are great. I wish there was one that guided you through the entire signup process.
Considering how many instances defederate and how their users hate each other, in reality it's not good advice to just pick any instance without learning about it 1st.
From the top 20 instances (https://fedidb.org/software/lemmy), there are 3 instances that are defederated or defederate a lot
All the other instances still federate each other.