Calgary has probably been the biggest rivalry for the franchise, as it has lasted multiple generations. In the 04-10 time I think it was pretty strong both ways and I think both sides probably considered each other their biggest rival. We were competing for the division, a pretty exciting playoff series, and were both pretty competitive teams. The early 90s was pretty similar to that time too, although the epic battle of Alberta was still pretty fresh in their minds at the time. The 80s we probably barely registered on their radar at all as they were serious contenders and we were nowhere close, but we still had a pretty epic playoff series in '89.
With them, we had a first round series in '89, '94 and '04 all go to the 7th game OT. I think the cities are different in their personality, yet sufficiently close and have a lot of ex-pats living in either city to maintain the rivalry for future generations. I don't think we need Seattle for a rivalry as they would be a new franchise and I don't think the fans will get into it as much.