how to get the top 10 popular blogs

If I understand you correctly, something like this should help you.

global $wpdb;
$results = $wpdb->get_results( "SELECT post_author, SUM(comment_count) as comments FROM {$wpdb->posts} WHERE post_type="post" AND post_status="publish" GROUP BY post_author ORDER BY comments DESC LIMIT 10");

This will return you 10 authors of most commented posts (with highest sum of comments count of each post they have written).

I’m not sure if this is what you wanted though.