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

import collections
def solve():
    n = int(input())
    S = [int(i) for i in input().split()]
    m = max(S)
    for i, s in enumerate(S):
        if s == m and ((i != 0 and S[i-1] != m) or (i!=n-1 and S[i+1] != m)):
            return i + 1

    return -1
N = int(input())

for _ in range(N):
    print(solve())