Bonus answer.  You mentioned that you want to set the default based on the logged user.  If you have a lot of users, setting it from Developer's mode is not economical.  You can access the Settings >> Technical >> Actions >> User-Defined Defaults to set it for each user.

Hello,

if you set a condition (Type=Customer Invoice), it seems the default value is kept. You need to set this condition because there is a onchange on company_id that reset the journal id. 

Hi!

I managed to do that by adding a condition like Laetitia Gangloff asked.

But, when I create an invoice based on an order, this condition doesn't work. :-(

How can we really change the default journal for invoices please … ?