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 lis():
    return [int(x) for x in input().split()]
    
def intt():
    return int(input())
    
def st():
    return str(input())
    
t = intt()
for i in range(t):
    n = intt()
    a = lis()
    s = set(a)
    if len(s)==1:
        print(-1)
    else:
        maxx = max(s)
        count = a.count(maxx)
        if a[0]==maxx and a[1]<maxx:
            print(1)
        elif a[-1]==maxx and a[-2]<maxx:
            print(n)
        else:
            for j in range(1,n-1):
                if (a[j-1]<maxx or a[j+1]<maxx) and a[j]==maxx:
                    print(j+1)
                    break