I guess you meant Fuji X-S10. I have only used the XF10. Apart from brand differences, it is more like pen-f/gx-9 body vs EM1 body differences eg depends on the lenses that you want to use... A7C has the latest af from Sony. Sigma has now native primes 24-35-45-65 and Sony has 24-40-50mm prime lenses in addition to existing 28-35-55 and 85mm is also not big to use with A7C... There are also small Samyang 18-24-35-45-75 and Tamron primes... So there are lots of choices with different price levels as small primes. If you want longer reach, then bigger/beefier cameras might be better... I recommend to check them in a shop as size/grip is very personal.