I use Schwalbe Marathon Plus Tours, uber heavy, and probably a harsh ride, but they only flat about once every 3,000 miles in the harsh city environment where I commute.
Nothing else I've tried including Gatorskins, Gatorskin Hardshell, Top Contact IIs or regular Marathons holds up as well.
I'm a teacher, late for work for me means I have 25 kids piled up outside my classroom door when the bell rings. I try to leave myself an extra 20 minutes on the ride in in case of a flat but that doesn't always happen. So I'm all about no flats.