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())
def argmax(A):
    max = -1
    res = -1
    for i,a in enumerate(A):
        if a > max:
            max = a
            res = i+1
    if res ==1:
        for i in range(1,len(A)):
            res = i
            if A[i]!=A[i-1]:
                break
    return res
for _ in range(t):
    n = int(input())
    A = list(map(int,input().split()))
    if len(set(A))==1:
        print(-1)
    else:
        print(argmax(A))