I can't compare it to HAProxy, but nginx load balancing was probably the simplest and most reliable part of our web infrastructure, and did exactly what we wanted and needed. Never played around with SPDY, but I liked the various options regarding server weighting, SSL termination, and like you mention the ease of configuration. It wasn't too fancy, but solved a problem and solved it well.
Unfortunately we had to switch off of it due to PCI compliance concerns[1], but I'd use it again in a heartbeat.
[1] not because there were actual issues, but because other solutions were fully audited out of the box. I'm hardly surprised that we've had more issues with those solutions than we ever had with nginx, including the time when we barely knew how to configure the thing. One of the unavoidable hazards of PCI Level 1 :( We still use it for the actual web requests quite happily.
I love nginx. You stole the words out of my mouth re: simplicity & stability of nginx for load balancing. If there's one thing you can really nail like a pro while still a rookie (like me) it's configuring nginx to load balance.
We didn't have enough servers behind it to really deal with dead servers, to be honest. Seemed to detect a failed server and route around it quickly enough, and we have monitoring per server in place to go in and reboot the thing or whatever.
The configs are pretty straightforward, but might get a little nuts if you're dealing with hundreds of servers behind the thing. I don't have to wear a sysadmin hat too frequently (thank god) but when I did it was pretty easy to deal with.
Huge fan of the fact that reloading the config would perform a configtest automatically before trying to apply the new settings. I don't know why all software doesn't do this.
I don't know too many details as I wasn't on that side of the PCI audit (more handling the software we write), but my impression was that off-the-shelf hardware was already certified where nginx was not. It was also one less component for us to manage, as we opted for hosting where we manage our web stack and the hosting company deals with the hardware and network.
Unfortunately we had to switch off of it due to PCI compliance concerns[1], but I'd use it again in a heartbeat.
[1] not because there were actual issues, but because other solutions were fully audited out of the box. I'm hardly surprised that we've had more issues with those solutions than we ever had with nginx, including the time when we barely knew how to configure the thing. One of the unavoidable hazards of PCI Level 1 :( We still use it for the actual web requests quite happily.