If they are the same price go for the Grob, I have flown both and the Grob is much better. More powerful, faster; its a proper aeroplane with good handling and aerobatic capability. There's a reason the RAF use them as their basic trainers!
Yes nav is a little bit easier with a high wing, but you also lose visibility in the turns with a high wing which as a current C182 driver I can say I actually find quite annoying. I learnt on the low wing PA28 and I don't think it was a major disadvantage when learning nav, if you ever needed to see what was below the wing you could always just move it briefly.