As the S9 may come out early in 2018, is it worth buying an S7?
My main reason for changing phones I my camera is ok but not great on the current phone. By all accounts the s7 and s8 have identical camera setups (or as close as makes no difference).
I prefer smaller handsets so the 5.1 vs 5.8 doesn't concern me in screen size, but I'd like decent battery life (A day of use), a good camera, and a phone that's not too slow. currently use a P2 from the UK with band 28 etc and the SD625 is fine, battery is unbeatable, but camera is only ok.
A shop near me is selling a boxed unused unlocked (ex optus) S7 for $399, so pretty cheap, and it's got the balance of AU warranty
S7 for $399 is a no brainer. You could go with Xiaomi Mi6 if you want a top-end device that's smaller, but you'll lack local warranty and some LTE bands.
Other possible options include Oneplus 5 but it's a 5.5" device, display apparently not amazing (but most consider OK) and it has no SD card slot.