Electra Jailbreak supports all devices with iOS 11.0-11.4.1. It can also be installed on Apple TV with the corresponding tvOS versions.
Chimera Jailbreak supports all devices with iOS 12.0-12.1.2, 12.4. It can also be installed on Apple TV with tvOS 12.0-12.1.1.
Unc0ver Jailbreak supports almost all iOS devices 11.0-12.1.2, 12.4. The exception is devices with A12(X) processors, which are only partially supported. Apple TV tool is not supported.
Cydia or Sileo?
Electra jailbreak installs the Sileo tweak Manager by default, but you can still install Cydia manually and use both applications at once.
Jailbreak Chimera only supports Sileo. This decision was made by the developers to promote their Manager tweaks.
Jailbreak unc0ver yet only supports Cydia, but may soon come version Sileo compatible with this tool. The exact release date is unknown.
Cydia Substrate or Substitute?
Electra jailbreak uses Substitute to install tweaks, because Cydia Substrate does not support the tool.
Chimera jailbreak uses Substitute for the same reasons as Electra.
Jailbreak unc0ver uses Cydia Substrate since this is the only tool approved by developer Saurik. On the other hand, A12(X) devices will soon begin to be supported by Substitute, which may not be possible for Cydia Substrate.
Jailbreak Electra appeared long before the release unc0ver, and very rarely has any problems. Most likely, with the updates, the tool has only become more stable.
Apparently, with the jailbreak Chimera so far, too, there are no problems.
The same applies to jailbreaking unc0ver, which is stable with the release of the first beta v0.0.
Electra jailbreak supports fewer tweaks as many of them work with Cydia Substrate rather than Substitute. However, every day the number of supported tweaks is growing.
This also applies to Chimera jailbreak, because it uses Substitute instead of Cydia Substrate.
To jailbreak unc0ver available only tweaks, because most of them are made for Cydia Substrate. However, when the support device A12(X) due to Substitute, this tool will be on par with Chimera and Electra.
We have figured out the main differences between jailbreak tools, and now you can make a decision. We wait new Jailbreak iOS 13.