I use NameCheap. They seem to work -- haven't had any issues. Support was decent as well when I used it. I went with NameCheap mostly because I already had my domain registered through them and utilize
DDNS with them.
If this was strictly for CCTV, I'd look into generating your own certs. All that happens upon connecting for the first time on a device is a warning about trusting the source. The only reason I went with a CA is because I have a web server with Nextcloud running on my LAN (think Dropbox, except I own it with no monthly costs and my storage is limited only by what drives I shove in the server). I've found an alarming amount of use for it, so I pay the few-bucks-a-year for the CA cert to keep the self-signed cert warning at bay for folks who connect that aren't me (friends, family, a local business I work with for ease of uploading items to me for managing their site, etc). The bonus is this works with my CCTV setup by default given I already had this set up before even adding CCTV into the mix.
I don't have much experience with other CA's though, but best I can say is NameCheap hasn't given me much reason to look into moving elsewhere.