well, you only asked @Peter, so I do not know, if you are interested in other opinions… 
concerning Airtable and Google Spreadsheets there already is a statement here
but what about first describing your requirements?
how many tables do you plan to use?
how many rows do you expect to have for each table?
generally from a relational database point of view… in terms of speed I would suggest to use a professional database, which is MySQL, which additionally offers a lot of tuning possibilities, see for example https://www.mysql.com/why-mysql/performance/index.html
as a start you can try my MySQL solution here App Inventor Tutorials and Examples: MySQL | Pura Vida Apps
EDIT: some other opinions you can find in this thread
Taifun