Hi,
An older @mac account has the advantage that Trial or Lapsed Paid for accounts work as iChat IDs/Screen Names where as the MobileMe (@me.com) ones do not.
as MobileMe would then be paid for to work in iChat you get all the other services Apple offers with that.
You can use Both names.
In iChat > Preferences > Accounts you can set up as many AIM, Apple and Jabber IDs was you want.
In iChat 3 you can have one AIM/Apple ID logged in and one Jabber ID logged in at one time which gives you three Buddy list if Bonjour is On as well.
In iChat 4 you can use the "Use this Account" check box in Every account/Screen Name in the ichat Preferences > Accounts and have as many Buddy Lists as you have Screen Names.
I would say that one is "better" than another.
AIM ones can be a bit more anonymous and less email looking. (Also free)
@mac.com ones can be free if they were a trial or have lapsed (I must admit about not knowing if you convert it to a MobileMe account with the @mac.com name once you stop paying)
The @me.com one works as a trial for the first 60 Days. The trial has to be actively cancelled or you get charged but does come with the extra services.
Jabber IDs and GoogeTalk fall the same way.
10:53 PM Friday; February 27, 2009