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())
    a=list(map(int,input().split()))
    dom=max(a)
    cnt=0
    for i in range(0,n):
        if a[i]==dom:
            if i==n-1 and a[i-1] != dom:
                print(i+1)
                cnt+=1
                break
            elif i==0 and a[1] != dom:
                print(i+1)
                cnt+=1
                break
    if cnt==0:
        for i in range(1, n - 1):
            if a[i] == dom:
               if a[i + 1] != dom or a[i - 1] != dom:
                  print(i+1)
                  cnt+=1
                  break
    if cnt == 0:
        print('-1')