More enterprise focused. They have better support (because you pay them) and more integrations. You also get more control over your integrations as well.

Zapier has a much heavier focus on business apps. Less internet of things, more workflows and invoices.

For me it's that Zapier has a lot more control over the integration logic - Being able to conditionally operate on Trello fields and Google Sheets columns makes automation much more doable. To me it's like an advanced for of IFTTT when you need that extra power.

I still use IFTTT a lot for device to device work. But for APIs I find Zapier much more comprehensive.

I use IFTTT for non-work related personal tasks; mostly moving pictures around and some social media stuff. I use Zapier for business tasks.