It actually depends on what you are offering?
If you are offering some product to use for free, then Try it Free make sense. For example, if you want to provide free access to your software or apps like editor apps, antivirus or any, you just want peoples to try it for free so later on they might pay for more service then Try it free button is better.
But for login to website, apps purpose signup for free is appropriate.
If you wanna try some free and unique call to action buttons then I refer you to check:
Free CTA buttons.
