Blogs MU - display most popular and/or active groups

If I wanted to change the:
Homepage team/group features...controllable via theme options (random or by site admin group id choice).

to show most popular or recently active, how could I do it?

<?php
$fetch_group_mode = get_option('tn_blogsmu_home_feat_group_id');
if($fetch_group_mode == '') {
fetch_random_groups();
} else {
fetch_specific_groups();
}
?>