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 = list(map(int, input().split()))
    '''arr2 = arr.copy()
    arr2.sort(reverse=True)'''
    if len(set(arr)) == 1:
        print(-1)
    else:
        z = max(arr)
        if arr[0] == z and arr[1] != z:
            print(1)
        elif arr[-1] == z and arr[-2] != z:
            print(n)
        else:
            for kk in range(1, n - 1):
                if arr[kk] == z and (arr[kk+1] != z or arr[kk-1] != z):
                    print(kk+1)
                    break