I live in Vancouver, so I haven't actually stayed in many hotels (although I've drunk in most of their bars
).
The Hotel Vancouver is Vancouver's "Grand Dame" of hotels. Very traditional, but also very old with everything that comes along with it (smaller rooms etc). It's also about a 10 minute walk from the Convention Centre(s). If you want a true Vancouver experience (and if budget allows) I'd pick a hotel down by the waterfront. Choices in this department include the Pan Pacific, the Fairmont Waterfront, the Fairmont Pacific Rim and the Marriott Pinnacle. All of these are easily walkable to the Convention Centre(s). The Century Plaza used to be fairly tired - I'm not sure if it's seen an update in recent memory. It's also the furthest from the Convention Centre.