Shifter

Actuation

Mechanical

linkage or cable or both
mimics actuation used on motorcycle
+Cost [citation needed]
+Simplicity [citation needed]
+Robust [citation needed]
-Most implementations mean driver has to take hand off steering wheel [citation needed]
-Minimum shift time is longer [citation needed]
-Maximum shift time is longer [citation needed]
-Unable to convert to automatic

Electronic

solenoid
+OEM solutions available[1] (they can be expensive)
+simplest upgrade to automatic
I have no idea on shift times
-cost
-everyone knows electronics always go wrong

Pneumatic

pneumatic solenoid
Which gas to use

• N2
• compressed air
• CO2

Valving +OEM solutions available [2] +Actuation speeds [citation needed]
-safety (compressed gas can be dangerous)
-largest number of points of failures of all actuation methods [citation needed]
-inherently limited number of shifts per tank
-shift gas pressure can change when running low on gas

Automatic Shifting

not going to touch on driver controls (paddles or whatever)