How much more abundant are protons in the universe than neutrons?

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A lot. Most of the universe is hydrogen (and apparently dark matter, whatever that is).

6:1 ratio of protons to neutrons or so. I think estimates vary slightly, but this is theoretically what one would expect.

and it can vary considerably as you can convert a proton to a neutron and vice versa.

The ration 3:1 has also been quoted to me (I expect the figure I gave first is the "freeze out ratio" about 1 second after the BB).

and it can vary considerably as you can convert a proton to a neutron and vice versa.

 

But only in a bound state or situation where you have additional energy. Free neutrons are, of course, unstable.

 

So stellar and planetary matter will have more neutrons. Interstellar hydrogen will not. The question becomes, which comprises more mass in the universe? From ajb's answer, it sounds like interstellar hydrogen wins.

Hm, that would be another interesting ratio: that of normal (ie, not dark) matter in stars compared to interstellar normal matter.