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()))
    if len(set(a)) == 1:
        print("-1")
    else:
        c = max(set(a))
        if a[0] == c and a[1] != c:
            print("1")
            continue
        if a[n - 1] == c and a[n - 2] != c:
            print(n)
            continue
        for i in range(1, n - 1):
            if a[i] == c and (a[i - 1] < c or a[i + 1] < c):
                print(i + 1)
                break
