(Original idea from here)
Every user has one community that they're really active in, and (usually) have a lot of good questions/answers there as well. I suggest that user profiles have a "Featured Community" section, where a user's stats for a particular community of their choice be displayed.
The "Featured Community" area would be a small box showing the user's badge count and rep, with a link that takes you to their profile page for that website.
It would be placed right above the communities tab:
and "Communities" would be renamed "Other Communities" if it was enabled. (If the featured community is in the Communities tab already, the Communities tab skips over that site.) This would allow users to show the site they are most active in more prominently (even if it's not their highest-rep site.)
It would be disabled by default, and if a user hasn't picked one (because they are either new or haven't found the feature yet), on the Profile section of the user's page, it would say "Featured Community: You haven't chosen a featured community yet. Click here to set one." (This would be visible only to the user.)
The Featured Community could be changed or disabled at any time in Settings.
What do you think?