Democrats have a better chance of regaining control of the US Senate in 2020 than in 2018 because in

2020 Democrats have fewer vulnerable seats to defend.
The vulnerable Democratic held seats up in 2020 are MI (Peters-D),MN (Franken-D),NH (Shaheen-D),and VA (Warner-D). All of these US Senators will end up getting re-elected due to the 2020 Democratic Presidential nominee's coattails.
Republicans have more vulnerable seats to defend in 2020 than in 2018
The vulnerable Republican held seats up in 2020 are CO (Gardner-R),GA (Perdue-R),ME (Collins-R)-Democrats need to target Collins,NC (Tillis-R),and TX (Cornyn-R).
Gardner-CO loses to Polis-D or Perlmutter-D
Perdue-GA loses to Ossoff-D or Michelle Nunn-D
Collins-ME loses in the primary to LePage-R who then loses in the general election to Pingree-D
Tillis-NC loses to Debra Ross-D
Cornyn-TX loses to O'Rourke-D or Joaquin Castro-D
+5D
2018
Democrats have to defend FL (Nelson-D),IN (Donnelly-D),MO (McCaskill-D),MT (Tester-D),ND (Heitkamp-D),OH (Brown-D),VA (Kaine-D),WV (Manchin-D),and WI (Baldwin-D). All but Donnelly-IN and Heitkamp-ND get re-elected -2D
Republicans have to defend AZ (Flake-R),NV (Heller-R)and TX (Cruz-R). Democrats will pick up AZ and NV.
48D 52R
2020 Democrats pick up CO and NC and win the 2020 US Presidential Election.
2022-The most vulnerable Democratic held seats are CO (Bennet-D),NV (Cortez Masto-D),and NH (Hassan-D).
The most vulnerable Republican held seats are AZ-open,FL (Rubio-R),GA-open,NC-open,PA-(Toomey-R),and WI (Johnson-R)