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)
    continue
  maximum = max(a)
  answer = 1
  if a[0]==maximum and a[0]!=a[1]:
    answer = 1
  for i in range(1,n-1):
    if a[i]==maximum and (a[i]!=a[i+1] or a[i-1]!=a[i]):
      answer=i+1
      break
  if a[n-1]==maximum and a[n-2]!=a[n-1]:
    answer=n

  print(answer)