1
3
5 3 4
 6
5
5 3 4 4 5
3
1 1 1
5
4 4 3 4 4
5
5 5 4 3 2
3
1 1 2
5
5 4 3 5 5
 1
3
10 1 5

1
 1
-1
2
2
3
1
 1

for  _ in range(int(input())):
    n = int(input())
    arr = list(map(int, input().split()))
    if len(set(arr))==1:
        print(-1)
    else:
        ans = -1
        max = 0
        for i in range(n):
            if arr[i]>=max:
                if (i!=0 and arr[i-1] != arr[i]) or (i!=(n-1) and arr[i+1] != arr[i]):
                    ans = i
                    max = arr[i]
        print(ans+1)