Both [email protected] and [email protected] works. Whichever you use, you will get all your emails to your Gmail inbox. This way, you can sign up twice for any website without creating another email account.
And, if you want to sign up more than twice, you can use [email protected]. You can add whatever you want after the + symbol and you will get your emails in your [email protected] inbox.
This is very useful especially when you want to sign up for a website more than once without setting up multiple email accounts.