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())
    arr = [int(num) for num in input().split(' ')]
    if len(set(arr))==1:
        ans = -1
    else:
        x = max(arr)
        ans = -1
        for i in range(1,n-1):
            if arr[i]==x and (arr[i+1]!=x or arr[i-1]!=x):
                ans = i + 1
                break
        if arr[0]==x and arr[1]!=x:
            ans = 1
        elif arr[-1]==x and arr[-2]!=x:
            ans = n
    print(ans)