I have a Vios.

And it averages 9.4km/L pure city driving.
Why is my FC like that? Try going to and fro 5-km places passing by EDSA during rush hours, with AC at almost max temp, and an average speed of at a maximum 20kph... let's see if the FC's don't drop below 10km/L.
With moderate traffic, I can easily do 11km/L without putting so much effort. One vios owner turns the engine off on traffic and does 13-14km/L on short trips.
At traffic, NO CAR IS EFFICIENT. Yun 11-12km/L mo lahat yan traffic? Try mo lahat traffic ta's short trips (short trips make the car gulp fuel)
Pero kung gusto ng Rio, yep, I think the best bet is the 1.2L MT or the 1.4L MT Sedan. Yan nalang ata yun sobra minimal ng FC issues. Mostly naman kasi isolated sa hatchback owners... Yun Sedan owners sobra onti ng may reklamo sa FC.