You can have up to 30 games/features saved in your Favourites, so I thought I'd share what I've found gives the best rewards (either to add to collections or resell) over time for anyone struggling to get a good process down. To favorite a game, hover over it in the Games list and click on the star icon. To remove that favorite, visit the Favourites star icon at the top and then click on that same game's star when you hover over it. Then, you can check the Favourites page periodically and click on "Hide Unavailable" to get a quick list of what you can do in that moment.
All of these are free unless otherwise indicated!
[ - - - Features Games - - - ]
1. Ant Hill (once per day)
https://www.marapets.com/ants.php
5. Clothing Rack (once per day)
https://www.marapets.com/rack.php
6. Genie (once per day, 4th wish resets the count)
https://www.marapets.com/genie.php
7. Giveaways (once per hour if you have less than 1mil MP, otherwise once every 2 hours)
https://www.marapets.com/giveaways.php
8. Grave Robbing (every 3 hours when asleep)
https://www.marapets.com/graverobbing.php
9. Guillotine (every 16 hours, may turn your pet Headless so if you don't want that result, only put a pet in who can't be costumed Headless)
https://www.marapets.com/guillotine.php
10. Nutty Tree (every 4 hours)
https://www.marapets.com/nuttytree.php
11. Operations Portal (once per day, may change species or costume)
https://www.marapets.com/portal.php
13. Photo Parlour (costs 1,500 MP every 12 hours and photos can make a good profit, so might not always need to do if you already have all your pets' photos collected/ to sell)
https://www.marapets.com/photo.php
14. Pot of Gold (once per hour if you have less than 1mil MP, otherwise once every 2 hours)
https://www.marapets.com/potofgold.php