There has been a number of threads on this topic over the years (in fact what I write below is largely copied from an earlier thread):
https://www.caminodesantiago.me/community/threads/travel-insurance.22998/#post-176680
http://www.caminodesantiago.me/community/threads/health-insurance-recommendations.12867/#post-101305
http://www.caminodesantiago.me/community/threads/medical-insurance.7980/
http://www.caminodesantiago.me/community/threads/health-insurance-recommendations.12867/
http://www.caminodesantiago.me/community/threads/travel-insurance.5676/
Despite some bad recommendations, I have had Medex in the past (it's recommended by the University where I work), but never needed it, thankfully. I have seen some good reviews of it as well.
A friend of mine did some really careful comparison shopping and was shocked to find huge differences in the fine print. I told this story on an earlier thread, but I'll reprint it here because it's kind of shocking:
One provider lists among benefits: "arrange for medical evacuation to home country" and "arrange for repatriation of remains to home country."
My friend asked: Does "arrange for" mean "pay for" or does it mean "call around to find someone to do it and send the client the bill?" The response: for medical evacuation, it means the latter; for human remains, it means the former. So, they will pay for your body to be returned, but will only find someone to bring you home if you are alive. Of course, that's what a live person said on the phone, which is not going to do you any good if the small print on the policy says otherwise.
If you have decent medical insurance at home, you will likely be covered at least for emergencies abroad, so I have decided that the main thing I need insurance for is medical evacuation and repatriation of remains, but it's worth checking carefully. And I have also learned that my credit card provides some of this, so after a couple years purchasing travel medical insurance, I have stopped. Like Laura says, it's impossible to know if your policy is really any good without first hand reviews from people who actually needed help. And in these threads there are a few of those testimonials.
Buen camino, Laurie