We are currently using the Thudbuster ST on our Cannondale. My stoker says it's the best upgrade we've made to the tandem. However, I recently found the ShockStop Seatpost from Redshift. Looks like a pretty cool idea. Not available until January 2019, but I'm keeping my eye on them. Will probably try one once they become readily available (and hopefully offer more than just 27.2mm with shims).
https://www.indiegogo.com/projects/s...ports-design#/
