Not to mention the vast ecosystem of some really great nginx plugins. The one thing I have found desperately wanting in both nginx and haproxy is the support for real-time stats and filtering found in Varnish (supports HTTP only). I am absolutely hooked!

  // Query Times
  varnishncsa -F '%t %{VCL_Log:Backend}x %Dμs %bB %s %{Varnish:hitmiss}x "%r"'

  // Slow Queries
  varnishncsa -F '%t %{VCL_Log:Backend}x %Dμs %bB %s %{Varnish:hitmiss}x "%r"' -m "VCL_Log:SlowQuery"

  // Top URLs
  varnishtop -i RxURL

  // Top Referer, User-Agent, etc.
  varnishtop -i RxHeader -I Referer
  varnishtop -i RxHeader -I User-Agent

  // Cache Misses
  varnishtop -i TxURL

  // awesome dashboard
  varnishstat