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())
    a=list(map(int,input().split()))
    r=1
    for i in range(n-1):
        if a[i] != a[i+1]:
            r=0
    if r==1:
        print(-1)
    else:
        maxx=max(a)
        ind=0
        for i in range(n):
            if i==0:
                if a[i]>a[i+1] and a[i]==maxx:
                    print(i+1)
                    break
            elif i==n-1:
                if a[i]>a[i-1] and a[i]==maxx:
                    print(i+1)
                    break
            else:
                if (a[i]>a[i-1] or a[i]>a[i+1]) and a[i]==maxx:
                    print(i+1)
                    break
