I was on vacation on Spain with my girlfriend's family, who are from the US. They all had booked international roaming from T-Mobile US. Their speeds were so bad they couldn't even look up restaurants on Yelp. Meanwhile, I am on T-Mobile Germany, which since last year has free (and unthrottled, I think) roaming in the entire EU per EU law. My data worked flawlessly. It was even faster than the hotel WiFi, and I used it to tether to my laptop instead of using the WiFi.