R8 V10 is much better built than the ZR1, just look at quality and body finish.
ZR1 maybe faster and more fun to drive but R8 is by far one of the best supercars in terms of practicality and being easy to drive for anyone.If i wanted a car only for track i would choose the ZR1 but if i wanted a car for both road and track, i would definitely go for the R8.