Daniel said about 4 years ago on Multitenancy :
In this sense ... extracting to a new model company_user ... what do you think :
1) user choosing the current-company-id “in use” and keep at user model 
Database - level
Or
2) user choosing the current-company-id “in-use” and keep at cookies
Session - level
Positives and negatives between this 2 scenarios ? There is another Alternative ?