I personally prefer the Online QB. It allows me, and my clients, access to the books from any computer with an Internet connection. (Not tied to a software programs on a particular computer.) I have several clients utilizing QB Online. They each have their own account and I have a login for each.
If you are set on using the traditional QB version, but do not want to use remote access, and both you and your client have a copy of the same version of the program; one solutions I have utilized in the past is saving the QB data files to a Dropbox folder that is shared between myself and the client. This way when one of you accesses the books the others transactions will be present. It seems to work good for this client.
Best of Luck,
Julie