RROD hasn't really been much of a thing since the older fat models. If you have a slim Xbox 360 you're basically golden.
Corona, Jasper, and Trinity boards are widely considered the most reliable revisions. This coveres late fat and all slim models produced from ~2008 up to 2013. The "E" model introduced in 2013 is also pretty reliable, but some units are not good for modding.
They started becoming less prevalent throughout 2008, as manufacturers got better at working with RoHS-compliant solder and die shrinks meant less heat.
However, the failure rate for the early models was only 25%. An astronomically high number for any consumer electronic and 10x that of the Nintendo Wii, but still a minority of consoles. Plenty of people got "bad" consoles in 2006, 2007 and didn't have a failure until 2009 or 2010. There were also plenty of "refurbished" consoles floating around game stores and ebay for years that would eventually fail again.
Corona, Jasper, and Trinity boards are widely considered the most reliable revisions. This coveres late fat and all slim models produced from ~2008 up to 2013. The "E" model introduced in 2013 is also pretty reliable, but some units are not good for modding.