We sort fundraiser on index pages by what we call the Activity Score.
The activity score is our way of making sure that the most fundraisers which are currently active are shown first. It also ensures that even if you for a period or under a specific object (e.g. a project page) don't have any active fundraisers, we will show the fundraisers with most donations ever.
The activity scores is calculated as
Activity Score = (Total fundraised last 7 days) * 1 + (Total fundraised last 2 months) * 0.01 + (Total fundraised last all time) * 0.001
There are few additional rules, but the above is the essence of the activity score.