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 solve():
    n = int(input())
    l = list(map(int,input().split()))
    if len(set(l)) == 1:
        print(-1)
    else:
        a = [i+1 for i in range (len(l)) if l[i]==max(l)]
        if len(a)<=2:
            print(a[-1])
        else:
            try:
                for i in range (len(a)):
                    if a[i]>a[i+1]+1:
                        print(i)
                        break
            except:
                pass

for t in range (int(input())):
    solve()