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

t = int(input())
ans = ''
for j in range(t):
    n = int(input())
    a = [int(i) for i in input().split()]
    M = a[0]
    M_pos = 0
    for i in range(1, n):
        if M < a[i]:
            M = a[i]
            M_pos = i + 1
        elif M > a[i] and M == a[i-1]:
            M_pos = i
        elif M == a[i] and M > a[i-1]:
            M_pos = i + 1
    if M_pos == 0:
        ans += '-1 \n'
    else:
        ans += str(M_pos) + '\n'
print(ans)


