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 = list(map(int, input().split()))
    m = max(a)
    k = a.index(m)
    if len(set(a)) == 1:
        print(-1)
        continue
    if k != 0:
        print(k + 1)
    else:
        while k < n - 1:
            if a[k + 1] == m:
                k += 1
            else:
                print(k + 1)
                break
        if k == n - 1:
            print(n)