Unfortunately as part of our ongoing site upgrades we have had to remove our support for linking external Steam accounts. If you are unable to login using Steam, please use the username/email address associated with your account to request a new password to login with here.
Nvidia's ShadowPlay and AMD's ReLive are only applicable if you have a graphics card that supports them. They will offer less performance overhead than other options, because they use hardware on the card to do some of the work rather than the CPU, but this comes at the expense of rather fixed settings and a fixed, lesser quality.
XSplit is paid software, but from what I've heard of it from those that use it, it seems very good. I use OBS Studio myself, it's free and works fine for what I do with it.