The R certainly does look sportier (I think) but what are the main differences?
In a nutshell :-
To driveThe GTi is lighter, more nimble and "chuckable" around the bends - slightly more fun on the twisties in the dry.
The R is (and feels) heavier, but has much better traction in all conditions, and is faster.
To buyThe R comes as standard with Xenons, 18" Alloys, LED rear lights, Front LED DRL's, Side skirts, R suspension and upgraded brakes, plus of course a 270ps engine and AWD.
CostsAs P3eps says above there will be very little difference in running costs, but the GTi will be slightly cheaper over a year.
The key decision is whether you want the AWD, which offers superb traction in all conditions but at the cost of increased weight (& purchase cost over the GTi

)
If all you do is travel up and down the motorway the R would'nt offer anything much over the GTI IMHO. But if you lived & drove in the Scottish Highlands, then the R would be my choice everytime