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

a=int(input())
for i in range(0,a):
    t=int(input())
    arr=list(map(int,input().split()))
    if(len(set(arr))==1):
        print(-1)
    else:
        k=0
        m=max(arr)
        for i in range(1,len(arr)-1):
            if(arr[i]==m and (arr[i-1]<m or arr[i+1]<m)):
                print(i+1)
                k=1 
                break
        if(k==0):
            if(arr[0]==m):
                if(arr[1]<m):
                    print(1)
            else:
                print(len(arr))     