If you read the review from Tom's Hardware from Thursday, it looks like maybe the actual choice isn't there yet.
Samsung Unveils GSIII Complete with Own Version of Siri
"with ......HSPA+ support
(Samsung is also working on an LTE mode)"................
Samsung plans to launch this baby in 145 countries and
is partnering with 296 mobile operators around the world to do so.
The 3G-only model will launch in Europe at the end of this month, and the 4G model will launch in North America, Japan, and Korea during this summer"
Reading that gives the impression that
1) the 4G versions is some way off yet
2) if Samsung are teaming with that many network companies, then getting an unlocked one may not be so easy at first as you think. It would be interesting to see a list of those operators
3) the story clearly indicates support for HSPA+, but the way its written, LTE support could well be vapourware, or at least for the near-term