10x15 pan or 12x17 pan for these amounts?

I hope you get an answer from Erin, who wrote the original recipe. I believe the recipe will work in either pan, because the volume of each pan is the same. I wonder if the two sets of directions are because there are differences in the sizes for cutting of the strips? At any rate, you can use whichever pan size you have. I would use the shorter pan for a traditional roulade, myself - because a skinny buche de Noel looks funny. But taste is what matters, along with what size pan you already own.