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

TC = int(input())
for __ in range(TC):
    n = int(input())
    a = list(map(int, input().split()))
    tmax = 0
    for i in range(1, n):
        if a[tmax] < a[i]:
            tmax = i
        elif a[tmax] == a[i]:
            if a[i] > a[i - 1]:
                tmax = i
            if (i != n - 1) and (a[i] > a[i + 1]):
                tmax = i
    if min(a) == max(a): tmax = -2
    print(tmax + 1)
            