Spolsky recommends even split: https://gist.github.com/isaacsanders/1653078
It should be a legal entity now because equity is under consideration by at least one person now. Anything else creates more issues than it solves. Better to have a hard conversation that ends in a split now than after months of tiptoing around the landmine.
Good luck.
A more important question is how do you manage disagreements. Specifically, you wholeheartedly believe you should do XYZ and they believe wholeheartedly in doing ABC. You can randomly pick. each do your own thing. let the person with most experience in that area make decision and go against your gut. split up. Ask for advice and trust that advice.
someone has to be the tie breaker 49% 51% should be the split
Canonical answer: http://foundrs.com, aka the co-founder equity calculator.
If you have just met 1 month ago, your chances or not making it long-term are above 50%. I'm sure you're aware of that. What most people don't do, to follow-through with that fact, is to require vesting. There has to be a way for such an unstable team to blow-up and break up.