- v6 connectivity - Who do they peer with and how? Are they native v6 across their network and are they peering with other native v6 networks, or are they stringing together a series of tunnels.
- v4 connectivity - how far is your tunnel going to have to traverse. Same questions as above, but for v4
- Automation - if this is your first experience with v6, there's going to be a learning curve, and having the ability to quickly change the tunnel settings is handy
- BGP - depending on what you're using this for, you may want to announce your own v6 space, not all tunnel brokers allow this
Hurricane Electric meets all these. I've been running a few tunnels through them for a while now and have had no problems that weren't of my own making ;)
1And, FYI, HE has a tunnel broker in Germany – curiousstranger – 2009-12-06T08:06:08.913