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())
for _ in range(t):
    n = int(input())
    A = list(map(int, input().split(' ')))
    if len(set(A)) == 1:
        print(-1)
        continue
    x = max(A)
    y = A.index(x)
    indices = [i for i, j in enumerate(A) if j == x]
    res = y
    for i in indices:
        if i == 0 :
            if A[i+1] != x:
                res = i
                break
            else:
                continue
        elif i == n-1:
            if A[i-1] != x:
                res = i
                break
            else:
                continue
        else:
            if A[i+1] != x or A[i-1] != x:
                res = i
                break
    print(res+1)