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 howabido(l):
    a=l[0]
    for i in l:
        if i!=a:
            return False
    return True
def lekbir(l,n):
    m=max(l)
    if l[0]>l[1] and l[0]==m:
        return 1
    for i in range(1,n-1):
        if l[i]==m and (l[i]>l[i-1] or l[i]>l[i+1]):
            return i+1
    if l[n-1]>l[n-2] and l[n-1]==m:
        return n
            
t=int(input())
for i in range(t):
    n=int(input())
    l=input()
    L=l.split()
    for i in range(n):
        L[i]=int(L[i])
    if howabido(L):
        print(-1)
    else:
        print(lekbir(L,n))
    