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

for _ in range(int(input())):
    n=int(input())
    count=0
    a=[int(x) for x in input().split()]
    for i in range(n-1):
        if(a[i]==a[i+1]):
            count+=1
    if((count+1)==n):
        print(-1)
    else:
        m=max(a)
        if(a[n-1]==m and a[n-2]<m):
            print(n)
            continue
        if(a[0]==m and a[1]<m):
            print(1)
            continue
        for i in range(1,n-1):
            if((a[i]==m and a[i-1]!=m) or (a[i]==m and a[i+1]!=m)):
                print(i+1)
                break