As somewhat of a purist, I vote Lucida Grande. I tend to think many Mac users who've been around since OSX 10.0 (wow, 13 years?!) feel that this font is integral to the Mac interface, but I'm sure Helvetica will grow on me.
Another thing I hope to eventually get over is the feeling of being rubbed the wrong way whenever Mac OS is influenced by iOS. Helvetica is one example. Another was reversing the scroll direction by default on my mouse (Lion or Mountain Lion, can't remember at the moment) because it better mimicked touchscreen scrolling.
For now, in practical terms, the font is buggy with Firefox and looks awful, but Safari and Chrome look pretty good.