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())
for _ in range(t):
    n=int(input())
    a=list(map(int,input().split()))
    s=list(set(a))
    m=max(a)
    if len(s)==1:
              print(-1)
    else:
        if a[0]==m and a[1]!=m:
            print(1)
        else:
            for ite in range(1,n):
                if a[ite]==m and (a[ite-1]!=m or a[ite+1]!=m):
                    break

            print(ite+1)
