I recommend using one single database for all the companies. You can add one additional column in the tables to identify/differentiate the company the data belongs to. In the long run, this approach will benefit you.
If you keep separate databases for each company, then on a later date if you need to prepare comparison reports then it is going to be cumbersome connecting with different databases. I am not saying that it is not possible to connect to different databases and prepare comparisons. If the count of the number of company's increase in the future this is going to make things much harder for you.
If you keep a separate database for each company, then any change in the structure of the table OR any change in the stored procedures needs to be updated on all the databases. The chances of making mistakes are high and as days go by maintenance becomes a nightmare.
If you go for one single database model then just keep a public variable in your PRG to identify the CompanyID while starting your application, then let each SQL query/update contain this CompanyID
Regards
Anser