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 i in range(int(input())):
  n=int(input())
  arr=list(map(int,input().split())) 
  if(arr.count(arr[0])==n):
    print("-1") 
  else:
    x=arr.index(max(arr))
    y=x
    while(1):
      if(x+1==n): 
        break
      elif(arr[x]==arr[x+1]):
        x+=1
      else:
        break
    if (x+1==n and x!=y):
      print(y+1)
    else:
      print(x+1)