Istio is the most popular Service Mesh. But API Gateways are also very important components in the Cloud Native mix. But if you go for a completely separate tool for API Gateway requirements and for other stuff use Istio, then you effectively have to maintain two different tool and build the expertise in your team for two different disciplines. But Istio can take care of almost all your API Gateway requirements(except for a few).
Will describe how you can leverage the Istio native CRDs to make Istio your API Gateway.