[iraqiboy90]

After careful reading on the php code at member.php, I found something...
I know this is a year old thread, but, here is another solution than to remove the "All" tab:

Add new plugin

Product: vBulletin
Hook Location: member_execute_start
Title: anything...
Execution Order:
Plugin PHP Code: $_REQUEST['type'] = 'user';

This will make the user subtab on the activity stream to be the default to be shown.