hr,
The Frontier ED 8x42, Sapphire ED 8x43 and 8x42 and now the Frontier ED-X 8x42 will all give you clear sharp images, but they do differ in other ways. Individuals seem to have a particular preference for either the dual hinge or single hinge designs. I generally found the grip and balance better on the slightly shorter single hinge, but distance between your eyes (IPD), or size of hands might make a difference to your choice. The slightly shorter single hinge models have a bit more field curvature and edge astigmatism and it seems a little less distortion to my eyes than the x43s but the differences are small and you may not notice it. The main difference between the Sapphires and the original Frontier ED was the improved colour profile, but not everyone on the forum appreciated the change. The Frontier ED-X seems different again. It might be just a batch difference, but the last ones I tried were a bit stronger in the yellow than I recall the previous models were. The particular examples I tried also had a bit of glare, probably due to slightly shiny interior surfaces, so something to look out for.
Whereas the Hawkes are made in China, the Opticron Countryman HD+ and the latest Natura ED are made in Japan and come with a 30 year warranty. It probably makes little practical difference these days, but Opticron have been working with the manufacturers for decades and have confidence in the engineering and availability of parts. However Japanese stuff usually costs a bit more and the competitive pricing of these models probably reflects a simpler optical design than the Hawkes. The most obvious difference is the field of view and degree of field curvature. I'm afraid I haven't checked out these two since their latest upgrades, but I rather liked the previous incarnation of the Countryman.
David