[vnabhi]

Go for Santro if you want:-
1. Fast acceleration in lower gears, esp in city driving.
2. Driving long distances---the driver's seat offers better comfort.
3. Better visibility, as the A pillar does not hinder your view.
4. Seating 3 passengers in the rear.

Go for WagonR if you want:-
1. Better ride quality, including the rear seats. I've heard horror stories of rear suspension in the Santro.
2. More space--in the boot, and on top of your head.
3. Lighter and effortless steering for city driving.
4. Better braking.
5. Reclining rear seats (a big hit that made me go in for a WagonR, but I'm not sure if this feature still exists)