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)
    else:
        m = max(a)
        p = a.index(m) + 1
        for i in range(1, n - 1):
            if a[i] == m:
                if a[i - 1] != a[i] or a[i] != a[i + 1]:
                    p = i + 1
                    break
    
            
        print(p)    
                
    
    
