Choose .com when
You want the most broadly familiar option, sell beyond a technical audience, or expect the company to grow into multiple categories.
Choose .io when
Your audience is comfortable with technology-focused branding and the .io version gives you a materially cleaner name than the available .com alternatives.
Protect against confusion
If another active company controls the matching .com, consider whether users may repeatedly navigate to the wrong site. Brand conflict matters more than extension fashion.