[kisielk]

[e-mail] is at least a distinct email address, unlike using +. Especially if you use different passwords for each account, it means if one of the emails is compromised then the attacker can't use it to recover passwords of your other sites.

[oijaf888]

+ can be a distinct email address, just as . can be an alias. It really depends on how your email server is configured. Postfix makes it really easy to adjust what character you use.