So for my personal projects, I use lets encrypt. As far as I know (and I could be wrong now, haven't checked in a while) - their certs are
only good for 3 months. Which is simple enough to get around - run a script on your box that updates the cert every 90 days automatically.
At work, we use a paid certificate that is good for a longer period of time (normally a year). So that's one benefit to paying, I suppose.
As far as encryption technologies and security, the traffic encrypted by a lets encrypt cert is just as secure as the traffic secured by a paid-for CA signed cert.