Of the presidential candidates, some currently hold office (Senate: Dodd, Obama, Clinton, Biden; House: Kucinich; Governor: Richardson) and some don't (Edwards, Gravel ).
For the ones who actually hold office I've been much more interested in what they do as officeholders than what they do as candidates. They all say they're great leaders, but some of them currently have the office, stature, and especially for Clinton and Obama, the hefty soapbox from which they can actually ... lead. They have the power to take something which is an issue right now and run with it, instead of thinking about all the wonderfully yummy things they'll do... if they win... 15 months from now.