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

t=int(input())
while(t>0):
    t-=1
    n=int(input())
    l=list(map(int,input().split()))
    if(len(set(l))==1):
        print(-1)
        continue
    ans=0
    m=0

    if(l[0]>l[1]):
        m=l[0]
        ans=0

    for i in range(1,n-1):
        if(l[i]>=m and (l[i-1]<l[i] or l[i+1]<l[i])):
            m=l[i]
            ans=i

    if(l[n-1]>l[n-2] and l[n-1]>m):
        m=l[n-1]
        ans=n-1
    print(ans+1)
