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())
    arr = list(map(int, input().split()))
    b = max(arr)
    if arr.count(b) == len(arr):
        print(-1)
    elif len(arr) >= 2:
        if arr[0] == b and arr[1] != b:
            print(1)
        elif arr[-1] == b and arr[-2] != b:
            print(len(arr))
        else:
            for i in range(1,len(arr)-1):
                if arr[i] == b and (arr[i-1] != b or arr[i+1] != b):
                    res = i+1
                    break
            print(res)
    else:
        print(1)