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

ans = []
for t in range(int(input())):
    n = int(input()); a = list(map(int, input().split()))
    if len(set(a)) == 1: ans += [-1]
    else:
        i = 0; x = max(a)
        while a[i] < x: i += 1
        if i != 0: ans += [i + 1]
        else:
            while a[i] == x: i += 1
            ans += [i]
print(*ans, sep = '\n')