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

def main():
    t = int(input())
    for _ in range(t):
        n = int(input())
        a = list(map(int, input().split()))
        M = max(a)
        occs = a.count(M)
        if occs == n:
            print(-1)
        else:
            if a[0] == M and a[1] != M:
                print(1)
                continue
            if a[-1] == M and a[-2] != M:
                print(n)
                continue
            for j in range(1, n - 1):
                if a[j] == M and (a[j - 1] != M or a[j + 1] != M):
                    print(j + 1)
                    break
main()