The earliest known looping coaster was in 1846 according to this...
It wasn't a circuit... just an inclined track and a loop.
www.ultimaterollercoaster.com/coasters/history/start/history_early.shtml
I've never ridden it. In fact I've never been anywhere near Japan, but I think this coaster is the most beautiful I have seen. It's the White Cyclone at Nagashima Spa Land.
But I would also like to nominate Nemesis at Alton Towers, UK, purely for its fantastic theming and attention to detail.
ahh well... I can still hope for something cool there! This pic is quite a long way out of date after all... the reclaimed area might be bigger by now!
and SAW the ride does look fantastic
http://www.projectdylan.co.uk/Construction/125