It really depends on what you are trying to achieve, what your budget is, and where you are in your model development cycle.
Nevertheless, I would recommend starting in self-service mode with the simplest tool you can find. This might be something like CVAT, though there are a number of other options (paid, free, SaaS, etc.) out there that a simple google search will return. Once you're ready to scale, you might want to consider handing off your annotations to specialized company like Sama. And yes, we also do 3D annotations. :)
(disclaimer: I work for Sama)