which sandbox is better for development : partial copy or full copy?

The short answer is neither of them is explicitly used for development.

We generally use a developer sandbox for development. Partial and full copy are generally used to test your code on real data from production.

For differentiation between partial and full copy sandboxes,

Partial Data Sandbox
Partial Data sandboxes include all of your organisation's metadata and add a selected amount of your production organisation's data that you define using a sandbox template. A Partial Data sandbox is a Developer sandbox plus the data you define in a sandbox template. It includes the reports, dashboards, price books, products, apps, and customizations under Setup (including all of your metadata). Additionally, as defined by your sandbox template, Partial Data sandboxes can include your organisation's standard and custom object records, documents, and attachments up to 5 GB of data and a maximum of 10,000 records per selected object. A Partial Data sandbox is smaller than a Full sandbox and has a shorter refresh interval. You can refresh a Partial Data sandbox every 5 days.

Full Sandbox
Full sandboxes copy your entire production organisation and all its data, including standard and custom object records, documents, and attachments. You can refresh a Full sandbox every 29 days.
Sandbox templates allow you to pick specific objects and data to copy to your sandbox, so you can control the size and content of each sandbox. Sandbox templates are only available for Partial Data or Full sandboxes.

For more info on when to use which sandbox, you can refer to:

https://help.salesforce.com/articleView?id=create_test_instance.htm&type=0

Hope this helps.