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())
    a = [int(i) for i in input().split()]
    dominant = max(a)
    if len(set(a)) == 1:
        print(-1)
    else:
        ans = 0
        for i in range(n-1):
            if a[i] == dominant and a[i+1] != dominant:
                ans = i
        if ans == 0:
            for i in range(1,n):
                if a[i] == dominant and a[i-1] != dominant:
                    ans = i
        print(ans+1)