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

for _ in range(int(input())):
    n=int(input())
    l=list(map(int,input().split()))
    if len(l)==1:
        print(l[0])
    elif len(set(l))==1:
        print(-1)
    else:
        x=max(l)
        if l[0]==x:
              for i in range(len(l)):
                  if x>l[i]:
                      break
              print(i)
             # print('hi')
        elif l[-1]==x:
            for i in range(len(l)):
                if l[i]==x:
                    break
            print(i+1)
        else:
            for i in range(len(l)):
                if l[i]==x:
                    break
            print(i+1)
            