The one outside Chrome, with its lack of sandboxing is plain unsafe. Its uninstalled from mine and my families computers, and if we need Flash then we use Chrome.
For OSX, here's the uninstall instructions.
And for Windows.
Friends don't let friends run Flash outside of Chrome.
If you must use Flash outside Chrome, and use with Firefox, the also install the noscript plugin and flashblock addons, so you can actually control when it runs. Also on Firefox you can disable Flash:
And finally, Chrome has a very handy "click to play plugin" feature. You should use it! In a Chrome tab type "chrome://settings/content", scroll down and change to "click to play"