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 i in range(t):
    count = 0
    n = int(input())
    arr = list(map(int,input().split(" ")))
    if len(set(arr)) == 1:
        print(-1)
    else:
        maxm = arr[0]
        imax = 0
        for i in range(1,n-1):
            if(arr[i] > arr[i+1]) or (arr[i]>arr[i-1]):
                if(arr[i]>=maxm):
                    maxm = arr[i]
                    imax = i
        if(arr[0] >= maxm) and (arr[0]>arr[1]):
            imax = 0
            maxm = arr[0]
        if(arr[n-1] >= maxm) and (arr[n-1]>arr[n-2]):
            imax = n-1
            maxm = arr[n-1]
        print(imax+1)