In a recent project, my client wanted to be able to select default value for product custom option. This is not a feature which is supported by Magento and it requires us to have some customization.
I created a module called "CustomOption" which allows admin to select default value for custom option of simple product. This module is developed simply and easy to use. In the backend, you can find a menu where you can select default value for all custom options of simple product. Go to Product Options > Manage Product with Custom Options:
Click on a product, you can select default value for each custom option.
Once you save this option in the backend, the value will be selected by default in product detail page in frontend. Here is how it shows in our site:
Well, I hope that you understand the goal of this module. Finally, here is the link for you to download this module. If you have any problem when installing and using this product, please do not hesitate to let me know.
P.S: We make this extension available in Git so everyone can make changes and improve the module: https://github.com/magebuzz/Magebuzz_Customoption