Don't make this harder than it is....no need to list caches. Go to your list of found geocaches....in the grid at the top of the list, click on the little blue ribbon. Your finds will then be sorted by favorite point. If the first 20 listed have 20 or more favorite points....YOU QUALIFY for this challenge!
Or.....Use the Challenge Checker.
A Favorite can mean many different things. It could mean that the location is interesting or unusual in some way, or that the hiding place or geocache container itself reflects the creativity of the geocache owner. The one thing you can say for certain is that the overall quality of the geocache is likely to be above average. Geocaching Favorites is a simple way to track and share the geocaches that you enjoyed the most.
If you are a premium member, for every 10 geocaches that you find, you are able to award 1 favorite point to a geocache in your find history. The Favorites accumulated by a geocache are displayed in search results and on the geocache page so everyone can see which caches stand above the rest.
Just make sure you qualify before logging it found! Please use stealth and replace the cache carefully!
If you enjoyed the cache and have a Premium Membership then consider awarding it a Favorite Point. The more Favorite Points it has, the more others may be interested in doing challenges. Thanks!