I’ve tried Canon Premium Fine Art Smooth, Innova (forget numbers), and Moab Entrada - all excellent, but my search is over with Arches 88.
EDIT (to add to this): Aside from its vibrancy, it's very white without using any OBAs.
And while I haven't used any other 44" rolls (just got the Pro-4100 a couple of months ago), it's very nice to handle - that is, it's flexible and durable, and it doesn't curl up. I think that's because it's made out of cotton.
The other papers I've used certainly aren't dog poop, but for me this is the winner - even at $425 a roll.
Have you compared the Canson Arches 88 to Epson Legacy Fibre? I am tempted to try the Canson Paper. I have tried the Red River Smooth Rag, and it is okay but in my opinion it is not as good as the Epson Fibre. I want to purchases 13 X 19 sheets to use with P900 and 13 X 19 sheets are apparently no longer available in Legacy Fibre.