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())
	array=[int(x) for x in input().split()]
	if len(set(array))==1:
		print(-1)
	else:
		dominant=max(array)
		for i in range(N):
			if array[i]==dominant:
				if i==0:
					if array[i+1]!=dominant:
						print(i+1)
						break
				elif i==N-1:
					if array[i-1]!=dominant:
						print(i+1)
						break
				else:
					if array[i+1]!=dominant or array[i-1]!=dominant:
						print(i+1)
						break