IRL I occasionally run experiments. So I decided to do a little sim experiment on a cruise from Venice to Athens last month. Project Fi on a nexus 6 on the beta channel with Nougat installed (mistake), one plus one with Piranha, Moto G with Toggle, My work phone with Sprint international, and my ipad mini with Tmobile data. TL;DR- The Piranha worked best everywhere, H+ speeds. T mobile also worked well at 2G but slow. Toggle was pretty good. Sprint was surprisingly good. And the Nexus 6 in the Beta program, started ok in Venice but got slower as we went. So I did a factory reset and switched out of Nougat, and it worked great once I did that. Piranha was more expensive but is more reliable now than when I was using it last year. Project Fi has a lot of promise, but was slow to register on the networks even after I did the Factory reset. But once it did register it would get LTE some of the time. This was in Katakolon, Santorini, and Athens. Toggle worked well in Italy and London. So my top 3 were Piranha, T mobile and project fi. This was Venice, Slovenia, Croatia, Montenegro, and Greece.