I voted the Sims, because I like the Sims. I had to stop buying the expansion packs, though, because they were gobbling up my comp's disk space, processor and RAM. Maybe one day, when I can afford an upgrade of some kind...[/wishful thinking] None of that tosh with the Xbox, though.
I'd vote Halo 2, but I've not really looked into the Halo serious. I was thinking about it, but then I got JSRF which has kept me amused for the last month. I'm looking forward to JSRF2, though, which will hopefully be appearing at E3 this year.