FullThrottle83 this is in no way a recommendation from the team, it's my personal opinion and I could be massively wrong. As a bit of background, I'm currently contracted by a company where we are building a social platform for a Dutch governmental agency with Flarum v2.0. I base the below on that experience alone.
Flarum v1.x
By far the safest option, battle tested. A wide range of extensions, more people with a wide field of knowledge. Customization is possible through css/less changes, an existing theme or through a custom theme (extension). Building extensions in Flarum v1 requires knowledge of backend and frontend development, and quite a bit of seasoned experience or skill. This is not wordpress..
Flarum v2.x
Very similar to v1, but a lot of improvements and optimizations, as well as upstream dependency upgrades like Laravel and Symfony. Although no actual commitment or effort was planned or executed on, some extensions are already slowly becoming compatible to v2. But the vast majority isn't soon and many probably won't ever be made compatible. Flarum v2 works, but new features might still be rough around the edges; this is especially true with direct messaging. Customization ought to be easier, but I can't really tell from my recent applied experience yet. Building extensions in v2 requires more knowledge in frontend development, now that webpack is bundling/splitting javascript files for performance reasons; it's another hurdle to take. Backend development is similar.
Currently I don't recommend using Flarum v2. Unless you don't install any extra extensions, can live with a broken installation for a while, are willing to create extensive reports whenever you run into issues and/or are capable to trace the issues. We're also not actively providing support for 2.x, and reports that come in without sufficient information could simply be ignored.
