I am sorry I can’t say anything about openvas_lib. The library is completely unknown to me. It’s not developed by Greenbone so you have to ask the author of openvas_lib for a comparison.
python-gvm is developed as the official python library for OpenVAS/GVM by Greenbone. Therefore if you want an up to date python library which is supported by the developers of OpenVAS/GVM you should choose python-gvm.