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

# Action is character. F. Scott Fitzgerald
# by : Blue Edge - Create some chaos

for _ in range(int(input())):
    n=int(input())
    a=list(map(int,input().split()))
    if len(set(a))==1:
        print(-1)
    else:
        m = max(a)
        i = 0
        while i<n:
            if a[i]==m:
                f = 0
                if i!=0:
                    f|=a[i]!=a[i-1]

                if i!=n-1:
                    f|=a[i]!=a[i+1]

                if f:
                    break

            i+=1
        print(i+1)
