The one advantage that Epson has had bragging rights over is the longivity of the prints. Kodak now has a universal paper (Ultima line) that gives you 100+ year print life from any printer. It comes in 15 and 40 page packs. I've picked it up at times on a buy 2 get 1 free sale and really like this paper. It's really heavy grade (71lb) and great for portfolio type work. I prefer the Satin over Glossy but that is a personal preference.
It's available at most places (Staples, Office Depot, Office Max etc). The only bad thing is the 4x6 version is actually 4x6.5 which can be a pain when trying to do edge/edge printing.
Make sure it has a Colorfast logo on the front of the paper.
A lot of Canon people really like Red River paper (
http://www.redrivercatalog.com) and it comes in big packs. They also provide less expensive large format paper.
Unless you need it now I would not get the 9100, a 9900 from Canon is coming soon and is supposed to be even more impressive with an added red, green tank. I would expect that the 9100 will drop in price very soon as this replacement is released (due in May). I use an 860 which falls in quality between the 9000 and the 9100 (not wide format) but produces really good prints.
Since there are so many versions and revisions of paper I would advise taking a sheet of your epson paper and going into a local store and running the demo on it. You can then be the ultimate judge.