If you’re scratching your head as you’re contemplating this question, I suggest that you relax.
This question isn’t at all what you need to think about.
Because it doesn't really matter.
Common sense tells you that a freelance translator is better because of advantages such as faster communication, lower rates, and direct interaction.
However, these features aren’t a function of being a freelance translator or an agency per se, but a function of one’s professionalism.
A freelance translator might be unexpectedly slow to respond whereas a translation agency might surprise you with quick replies.
By the same token, you can end up paying more to a freelance translator then you would to an agency for reasons such as inefficiencies.
You might be thinking that your translator is the one who's doing the actual translation, but in fact, I've seen translators delegate a lot of their work to other people, effectively functioning as an agency.
So, what should you focus on instead when you're looking for a translator?
I suggest that you focus not on making a choice between an agency and an independent translator, but on how professional a particular translation business appears whether it’s an individual translator or a company.
You can get an idea of their professionalism by looking at their website, references, recommendations, quality and relevance of their social media content, etc.
And professionalism especially shows in how they communicate with you when you contact them. So make sure to contact your candidates and talk to them to see how fast they reply and what kind of response they generally give you.
Do this and you will end up with a very good translation vendor—someone much better than the one you would find by concentrating solely on choosing between an agency and an individual translator.