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 " "*int(input()):
    a=int(input())
    b=list(map(int,input().split()))
    if len(set(b))==1:print(-1)
    else:
        k=max(b);p=0
        for i in range(a):
            if i==0:
                if b[i]==k and b[i+1]!=k:p=i+1;break
            elif (i==a-1):
                if b[i]==k and b[i-1]!=k:p=i+1;break
            else:
                if b[i]==k and (b[i-1]!=k or k!=b[i+1]):p=i+1;break
        print(p)