I'm not terribly experienced with Nginx, but HAProxy was (and is) a load balancer first where Nginx is a server with load balancing abilities (same as Apache can, though it gets less love these days). HAProxy has pretty powerful HTTP support and capabilities, however, so I'm not sure I buy the other argument in this thread.

HAProxy also allows you to modify balanced nodes while the server is running, and has fantastic logging once you get used to looking at it.