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 _ in range(t):
    n=int(input())
    arr=list(map(int,input().split()))
    count=set()
    for i in range(n):
        count.add(arr[i])
    if len(count)==1:
        print(-1)
        continue
    index=0
    maxx=arr[0]
    for i in range(1,n-1):
        if arr[i]>=maxx and (arr[i]>arr[i-1] or arr[i]>arr[i+1]):
            maxx=arr[i]
            index=i
    if arr[-1]>=maxx and arr[-1]>arr[-2]:
        index=n-1
    print(index+1)
    