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=set(a)
    if len(s)==1:
        print(-1)
        continue
    else:
        k=max(a)
        for i in range(n):
            if a[i]==k:
                if i!=0 and i!=n-1:
                    if a[i]!=a[i-1] or a[i+1]!=a[i]:
                        ans=i+1
                        break
                elif i==0:
                    if a[i]!=a[i+1]:
                        ans=1
                        break
                elif i==n-1:
                    if a[i]!=a[i-1]:
                        ans=n
                        break
            else:
                pass
        print(ans)
        

