2.1 Adam Smasher in 1 minute (DFTR Very Hard)
One of the faster Smasher fights after 2.1 is using stealth and netrunning. When fighting him guns blazing the Don't Fear the Reaper version can be around 4-5 minutes with a high damage build on Very Hard and much faster on lower difficulties. The DFTR Smasher also has the ability to one shot V on Very Hard. However, when using a netrunner combined with stealth takedowns the fight can be 1 minute or less. Stealth takedowns were not working on Smasher after 2.0 until the 2.1 update.
Although you don't need a netrunner to do stealth takedowns, it's slightly faster with memory wipe and an on demand blind from overclock with the Tetratronic Rippler.