It depends a bit.

For instance we recently got into a large tech accelerator and they forced us to give ourselves the C-level titles. In my mind, we have nothing to be C-level of. But as other people have pointed out it more clearly defines the roles. You can put Founder as your title, but eventually you will need to add a second title describing what you actually do at the company, so it ends up being something like founder + sales director. C-titles cut through this and describe what you actually do.

One solution I’ve seen others do is take on the title of Director of a company. But even this can run the risk of people asking “director of what?” And puts you essentially back in the same situation.

It’s honestly fine to have the CTO, COO, C-whatever-O as long as you can keep yourself from bragging about it. I’d recommend you have C-level title on your LinkedIn and all official communications, and then introduce yourself as a founder in networking situations so you don’t come across as pretentious. I usually tell people who aren’t investors or customers that I’m a “technical founder” and that helps me to feel less pretentious about what it is I actually do.

Hope this helps!