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()))
    m1,m2=max(a),min(a)
    if m1==m2:
        print(-1)
    else:
        x=1
        for i in range(n):
            if i==0:
                if a[i]==m1 and a[i+1]!=m1:
                    x=i+1
                    break
            elif i==n-1:
                if a[i]==m1 and a[i-1]!=m1:
                    x=n
                    break
            else:
                if a[i]==m1 and (a[i-1]!=m1 or a[i+1]!=m1):
                    x=i+1
                    break
        print(x)