If you could change the result of one senate race in favor of both parties in each election cycle

[Ferguson97]

Assuming each cycle is in a vacuum (ie, I can choose Susan Collins in both 2008 and 2020):

2008: North Carolina (she loses in 2014 anyway) and Kentucky (bye-bye, Mitch)
2010: Washington (fairly easy to win back in 2016) and Wisconsin (bye-bye, Ron Johnson)
2012: North Dakota (she loses in 2017 anyway) and Arizona (butterflies away Sinema)
2014: Virginia (easier to flip back than NH) and North Carolina (harder for Republicans to flip than any of the other options)
2016: Nevada (probably easiest to flip back) and Missouri (I like Jason Kander)
2018: West Virginia (Manchin retires in 2024 anyway) and Texas (easiest choice of my life)
2020: New Mexico (should be easy to flip back in 2026, even in a Biden midterm) and Maine (since I can't pick Doug Jones)
2022: Nevada (solely because Laxalt is the least insane of all the options) and Ohio (JD Vance is a cretin)