joey:
Since we all have different palates, "best" is pretty much meaningless. Start with the original, so you can become familiar with the Frog Morton profile. It's quite unlike any other latakia-based blends that I've tried. It is the belief of reviewer extraordinaire William Serad -- and I absolutely agree with him on this -- that the latakia in the Frog series has been treated as a cavendish -- that is, lightly sweetened/flavored. It gives all of these blends a unique flavor profile. They are fully English in design, with an aromatic element that really sets them apart.
My favorite seems to no longer exist -- at least, not as it once did. It's Frog Morton Across the Pond, which used to contain Syrian latakia; the current tins do not mention Syrian anymore. But I also highly recommend Frog Morton on the Town, which combines Cypriot latakia with Basma to develop a very subtle vanilla quality. It reminded me of Samuel Gawith's Perfection, but it was a smoother and more, well, refined blend. (Perfection adds vanilla to the blend, whereas a sense of vanilla seems to be the natural result of the cavendished latakia and the sweet Basma in FMOTT.)
To be honest, I have yet to try the original Frog Morton, so I can't comment on its merits specifically. I have an 11-year-old tin in the cellar I should probably get to sooner rather than later, though. Thanks for the reminder!
Bob