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 i in range(int(input())):
    n= int(input())
    l= input().split()
    l=[int(e) for e in l]
    nl= sorted(l)
    if nl[0]==nl[-1]:
        print(-1)
    else:
        m= max(l)
        for i in range(len(l)):
            if l[i]==m:
                if i==0:
                    if l[i]>l[i+1]:
                        print(i+1)
                        break
                elif i==len(l)-1:
                    if l[i]>l[i-1]:
                        print(i+1)
                        break
                elif l[i]>l[i+1] or l[i]>l[i-1]:
                    print(i+1)
                    break
                        