Q. Which variant is best? What would be service cost - Yaris?

I think it is the J. It gives you everything except for rear disc brakes, electronic stability control, rear AC vent, noise cutting side glasses, foldable orvms, running day lights, touchscreen, front parking sensors, tyre pressure monitor. Touchscreens are highly overrated and expensive. Maybe your dealer can fit them for you, but you have to ask who will be responsible for updating the software in it. The J variant gives you all 7 airbags, projector headlights. You can get fog lights, auto dimming irvm, tyre pressure sensor monitor fitted for much less than paying 1.5 lakh extra for the G variant.

Service costs are definitely lower than Maruti. However lately Toyota service centres have also started adding useless charges which they don't tell you about. You need to read the service estimate carefully before you hand over the car.

YarisCVTi. Being automatic service cost is lowest.