I'm in the same boat, I've built a camera and wondering what to put in it. I've done the first few shots with Kodalith, but I've only got so much of that to go around, and op is op.
With the demise (but hopefully the resurrection later) of Harman DPP it's negatives and contact prints all the way for me, my scanner can only take 8x10/A4 and my pinhole cameras go a lot bigger than that.
But I feel it's a bit of a waste to use real film, especially with the expense, there's no need for such high-resolution films when it's only contact printed and pinholes diffract the hell out of it anyway.
The only reason I can see to use film is for the speed. I keep seeing the same guy selling 320TXP in 5x7" for $1.50 a sheet on fleabay (it hasn't even expired yet) and contemplating whether to bite, until I compare that to MGiv at 40c a sheet in 5x7". Plus paper goes a lot bigger and stays relatively cheap (even 11x14" MGiv is only $1.70 a sheet).
Paper (esp contact-printed to paper positive) also gives a bit more 'rusticness' to the image imho, and isn't that what pinhole should be?