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 q in range(t):
    n = int(input())
    lst = list(map(int,input().split()))
    if(lst.count(lst[0]) == n):
        print(-1)
    else:
        maxv = max(lst)
        for i in range(n):
            if(i == 0 ):
                if(lst[i] == maxv and lst[i+1] != maxv):
                    print(1)
                    break
            elif(i == n-1):
                if(lst[i] == maxv and lst[i-1] != maxv ):
                    print(n)
                    break
            elif( lst[i] == maxv and (lst[i-1]!=maxv or lst[i+1]!=maxv)):
                print(i+1)
                break