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 t in range(int(input())):
  n = int(input())
  l1 = list(map(int,input().split()))
  gg=0
  mi = max(l1)
  if len(set(l1))==1:
   print("-1")
  elif l1.count(mi)==1:
    print(l1.index(mi)+1)  
  else:
    for i in range(n-1):
      if l1[i]==mi and l1[i+1]==mi:
        pass
      if l1[i]==mi and l1[i+1] !=mi:
        print(i+1)
        break
      if i!=0:
        if l1[i]==mi and l1[i-1] !=mi:
          print(i+1)
          break


