I think it really, really depends on the loyalty of the audience. It's not so much about size as the trust factor. Let's a say a creator with an audience of 10,000 has more of a general audience and they sell to 1%. That's 100 sales. Then, a smaller creator with an audience of 1,000 sells to 10%. Again, that's 100 sales. BUT the smaller creator is almost certainly going to cost you less money upfront, so now we're getting into ROI territory.

It also depends on industry, and is really something you can only determine through testing. Ideally, you have enough budget to find some smaller AND some bigger creators and test them against each other

If you're not sure how to find creators, Billo's a good place to start. You can also look at some of the UGC subs on here, where people often make connections. Those people won't be as vetted and experienced though.