Thanks for everyone's input so-far.
More details have emerged regarding the different networks:
Android Authority write up on HSPA vs LTE: Which one is better?
I'm not sure if this answers the question or questions the answer, though. However, at a glance it looks like the HSPA+ SGSIII will be the one to choose.
The HSPA+ flavour is supposed to also come equipped with a quad core, unlike the dual core that has been mentioned as destined for the LTE version. This may further seal my preference towards the HSPA+ unit, unless others here can suggest reasons otherwise.
And further details on the SGSIII:
Samsung Galaxy S III Gets Benchmarked
Any further comments on the "best" version to buy...the LTE or the HSPA+?