[Boshusan]

It depends, if you don't mind watching vintage stuff you can go with Jetman or Liveman, then jump on something from the 2000's (I suggest Gekiranger/Dekaranger), while catching on up to date ToQger at the same time to have a global idea about Super Sentai.

Jetman and Liveman have great vilains and some memorable nightmare fuel, despite the FX at the time. I'll suggest Jetman btw (just for Radiguet, that bastard you like to hate).
If you're fond on martial arts flicks pick Gekiranger, period.
Dekaranger has a good writing, as "Deka" is slang for "cop", it's set in a police affairs setting. Each episode can relate to a specific film or trope about police stuff, and there are many (hostage situation, going undercover, suspect survey, etc.) !