I've been using the printer for about 2 years, probably 90% for landscape prints and 10% general/portraits. Like most folks I experimented a bit initially and then settled on two papers for most of my work. For landscapes I'm using mostly Canson Infinity Platine Fibre Rag. This provides a lovely subtle surface texture and very good color gamut and D-max. For portraits I'm mostly using Canon premium fine art smooth, the 13 x 19" sheets. I have a 24" roll I haven't used yet, and apparently they aren't making it in that size anymore, which makes me sad because it's a lovely cotton rag paper with a good enough D-max.
I have a bunch of other papers I haven't even tested with the printer because these two do everything I need.