Customization in project management means something different to different businesses. For one it might mean making sure you can set up a proper reporting dashboard with exactly what you need on it to run your projects. While, to another, customization means taking a piece of software and making it look like it is a custom tool that was crafted by that business.
Asana has plenty of customization that will appeal to that first group above. You can customize your projects and workflows to basically whatever you need while using integrations to fill the void of everything else. However, with Wrike, you can meet the needs of that second group above by creating a white-label project management software with your own branding.
Customization is typically a very popular feature that many businesses require out of a project management tool. Your actual customization needs, and which group above you resonate with the most, will determine which tool is best suited for you.