You must ask yourself what you want to use them for.
For some things its enough to use TOR.
I2P for instance is already more secure and slower.
Public proxies might be open by accident.
Some are setup on purpose and have active logging and even worse.
For example hidemyass gave out there logs to govs on multiple occasions.
A russian no logging VPN for example might be appr for evil stuff.
Popping a box is another option