Active / Passive sensors

[Suicide Junkie]

In the unmodded game, all sensors scan with equivalent power.
Only the research costs, and build costs differ.

Thus, there will clearly be one uber-scanner tech, and you will never bother researching the others unless they are a prerequisite tech for some other component you want.

Some modded games (such as P&N PBW) have the cloaking system set up such that you will need multiple scanners to ensure you see everything.

P&N has gravitic cloak based on the mass of the ship (lighter ship = harder to see with gravitics)
So if you're trying to hide, you'll use a small ship, but then you'll not have enough space on the small ship to add cloaking protection against active and passive scanners!