You gave no valid reason to why a paid site would be so much better.I am referring to owning the whole site rather than the free version of it. I just assumed people would be intelligent enough to realize this. OP asked about free solutions vs. paid solutions. Using a custom domain on a wordpress.com account is still a free solution. Please try again.
They are two different situations. Paypal is just a service provider and you can switch any time.
A free blogging site can put you out of business when they like. But having your own site means you own your domain and nobody can do that.