Which one is better for Exchange performance "Distribution group or security group"?

A distribution group! it can be used for sending emails to a group of users. We cannot use distribution group for assigning security permissions. A user’s membership in many security groups could result in slow logon performance. Therefore distribution groups should be used wherever possible.

Distribution groups can be used only with email applications (such as Exchange Server) to send email to collections of users. Distribution groups are not security enabled, which means that they cannot be listed in discretionary access control lists (DACLs).

"Distribution Group"-Because it creats a separate mailbox for the group so that you could send emails to th whole group via one email address.-you could assign a group owner who can add a members to that group, you can use this for team and make team leadrs group owner.

A distribution group can be used for sending emails to a group of users.and Security groups can be used to assign security rights on resources inside your Windows 2003 Active Directory network. By using a security group, we can collect a group of user accounts in a department and assign them access to a shared folder. 

Distribution group for Exchange and Security group for Active Directory

Distribution group

Distribution groups are intended to be used solely as email distribution lists. These lists are for use with email applications such as Microsoft Exchange or Outlook.