I would say go for Ativa, I fitted my wife's car with a cheap TC and the power delivery is so sweat for city drive. Turbo lag is reduced.

Myvi, despite using the same D-CVT as Ativa, my mum's new car has this loud drone sound. Complained to SC and they answered it is the same for all Myvi variants => loud drone. Ativa has got almost no loud drone sound.

Secondly, all Myvi are fitted with very small front seats, hard to get comfortable when driving. Ativa on the other hand, has large front seats by Perodua standard.