What websites don't play well with Tor?

I occasionally encounter websites that don't play well with Tor. They may require a CAPTCHA, load very slowly, or reply that my IP address has been banned. Perhaps you've seen that too. Given periodic complaints on https://lists.torproject.org/cgi-bin/mailman/listinfo/tor-talk and https://tor.stackexchange.com/, such behavior is fairly common. Some websites seem worse than others. But it's hard to draw reliable conclusions based on anecdotal information.

I've decided to collect some data. I have a crude hack that periodically determines loading times for various URLs, while logging the Tor exit used for each with the Stem exit_used.py script from https://stem.torproject.org/tutorials/examples/exit_used.html. It uses "torsocks midori -s https://foo.com" to get PNG snapshots, and uses "host foo.com" to get IPs to link with the exit_used.py output.

I'm going to start with the top ~50 sites based on Alexa etc. If there are sites that you would like tested, please reply here, or email me directly.