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())
    A = [int(x) for x in input().split()]
    s = set(A)
    if len(s) == 1:
        print(-1)
    else:
        maximum = 0
        index = 0
        if A[0] > A[n-1]:
            index = 1
        else:
            index = n
        for i in range(1,n-1):
            if A[i] > maximum and (A[i] > A[i-1] or A[i] > A[i+1]):
                maximum = A[i]
                index = i+1
        if A[0] > A[n-1]:
            if A[0] > maximum:
                index = 1
        else:
            if A[n-1]> maximum:
                index = n
        print(index)
            