Hmmm... A difficult question and its a personal choice, but I might opt Wagon R; new model, K10B fuel efficient engine, modern looks, etc. but its tall body design isn't good when it comes to road grip and handling. Cultus wins here.
I think both are economical, when it comes to fuel efficiency and parts. Cultus may win here.
Of course these are worth buying, even if slightly (yes slightly, not more) expensive from the market.
You will get a certified vehicle, with peace of mind, and also some sort of warranty. What else one needs?
In any case, prefer a well-maintained vehicle, irrespective buying from Pak Suzuki certified cars or from open market.