Liana was discontinued due to some unknown reasons. However people face lots of difficulties in fixing Liana issues. Might be because of stupid mechnics. Many people sold their Liana.
Cultus is a car who has good re-sale, parts are easily available and maintainance is also cheep. Many road side mechanics can also fix this car however I dont recommend you to get work done from them.
Apart from this, Liana is bigger car and in my experience it is quite fast on CNG as well and on Petrol it runs like rocket. In short runs it can beat Hondas and Toyotas of same class. At high speed stability is issue and high speed torque is also missing. In simple if you want to use it as normal city drive, it is quite good. It is sedan and you will get a diggi which is quite useful thing which Cultus lacks.
But if your family is not big, then you should prefer brand new cultus over a used (and might be abused) Liana.