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())
def check(a):
    if a.count(a[0])==len(a):
        return False
    else:
        return True


for q in range(t):
    n=int(input())
    a=list(map(int,input().split()))
    m=max(a)
    ans=a.index(m)+1
    if a[0]==m and a[1]!=m:
        ans=1
    elif a[-1]==m and a[n-2]!=m:
        ans=n
    else :
        for i in range(1,n-1):
            if a[i]==m and (a[i-1]!=m or a[i+1]!=m):
                ans=i+1
                break
    if (not check(a)):
        print(-1)
    else:
        print(ans)
        
