I'd take the perennial contender route. I would much more enjoy watching 10 straight years of competitive, conference contending basketball than one year of possibly winning a championship. I say possibly, because obviously we would never really know the outcome, and if we did, I wouldn't watch at all. 10/10 chances of making the Finals or conference finals is better than 1/10 of actually winning it IMO.
I'd rather say I supported a team that went to the playoffs for 10 straight years and was a threat to get to the conference finals in each of those years than say I supported a team that sucked for nine years but then went out and bought a winning team for 1 year, and then proceeded to suck again afterwards. The former would also present the greater challenge IMO. And I'm talking at least a conference contender here, not just a team that squeaks into the playoffs year after year with a low seed.
Those Blue Jays championships were awesome, but the wasteland before and after is a little depressing, no?