Aeroo reports works with 9.0, but its future is uncertain - as far as I know there is no working port to 10.0 and Alistek, the company that created the engine, is not actively working it anymore. Developing reports with Aeroo is quite easy and convenient though, once you get it up and running.

Odoo Community Association is working on a py3o reporting engine (available at apps.odoo.com and GitHub) that also enables you to use Libreoffice for designing the reports. There is a working version for 10.0 but not 9.0. I have not tried this engine myself yet.

Developing reports for Odoo has always been a bit of an evolutionary process since technologies have come and gone (rml, mako, qweb, aeroo, py3o...). At the moment if you need cross-version compatibility between 9.0, 10.0 and upcoming versions, I would say learning more about QWeb would be the best choice since it is 1) chosen by Odoo S.A. so it works right out of the box on all versions from 8.0 onwards, and 2) used widely by developers, so you can also find help for possible problems more easily.