I just sold a C180 model 99. The car was bumper to bumper genuine and original. Used High Octane occasionally on 50-50 ratio otherwise used simple petrol.
Fuel average was 10-11 km/l within city and 13-14 km/l on mway if driving around 120-140 km/h
Note that the car was manual tranny.
Given the choice, I would go for merc as the driving experience is so different from Honda. You can simply feel the power. Also, this 90s model is not too complicated like latest models and you do not need to worry about maintenance coz a fit merc hardly needs any.
Hope it helps