I have a bit of a radical view on this:
In order to be successful you have 10 years full of work ahead of you. In comparison, whatever is there today is nothing.
If you are co-founders, then it should be 1/3 each and each with the same salary.
At least this should be the default. You may have different needs, experience and skill sets and can of course speak about these openly, but 1/3 each should be the default imho.