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

def testcase():

    n = int(input())
    arr = list(map(int, input().split()))

    mx = max(arr)
    for i in range(n):
        if arr[i] == mx:
            if i == 0:
                if arr[i + 1] != mx:
                    print(1)
                    return
            elif i == n - 1:
                if arr[i - 1] != mx:
                    print(n)
                    return
            elif arr[i - 1] != mx or arr[i + 1] != mx:
                print(i + 1)
                return
    print(-1)
    return


import sys, os
if os.path.exists('input.txt'):
    sys.stdin = open('input.txt', 'r')
t = int(input())
for _ in range(t):
    testcase()