Nginx really is more of a swiss army knife web tool. It does a lot besides just load balancing and reverse proxying, and those things it definitely does better

Nginx really is more of a swiss army knife web tool. It does a lot besides just load balancing and reverse proxying, and those things it definitely does better than HAProxy. AFAIK, you can't serve static assets with HAProxy, and HAProxy doesn't have any kind of caching built in, in addition to dozens of other features of Nginx that most people probably don't even know about. In the HA load balancer category I think HAProxy is clearly a more capable tool since that's all it's supposed to do, but there's not really a simple answer to your question.