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

# Har har mahadev
# author : @harsh kanani

for _ in range(int(input())):
    n = int(input())
    l = list(map(int, input().split()))
    m = max(l)
    i = l.index(m)
    if i==0:
        while i<n-1 and l[i]==l[i+1] and l[i]==m:
                i+=1
        temp = set(l)
        if len(temp) == 1:
            print(-1)
        else:
            print(i + 1)
    else:
        temp = set(l)
        if len(temp) == 1:
            print(-1)
        else:
            print(i+1)


