No contest. Factions give you perks and benefits that improve everything about the gameplay. And also without social interaction, I doubt you will play for the years required to get anywhere with your goals. There isn't really any benefit to solo play. Except fewer people will be bothered when you inevitably go inactive.
Especially early on, joining a faction helps your progress a lot.
Like if you joined my faction, we would immediately loan you a full set of combat armor and a decent weapon. And after 72 hours, you'd have access to unlimited free meds, candy, beer, etc. from our armory. All this is in addition to the perks you'd enjoy (which matter more later on.)
Be careful. All factions act like they are a great place to be, but if you pay attention, there is a fairly high degree of dysfunction in some and others can be outright toxic.
Make sure you understand the expectations for warring, chaining, training, etc before you join. Having one that understands RL comes first is a good idea as well.
factions are great because they provide perks, support, and people who have your back obviously, there's standards you have to uphold so you have to be ready for commitment, but it's definitely worth it to join a faction