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())
l=[0,1]
for i in range(2,1000):
    l.append(i*i)
while t:
    t-=1
    n=int(input())
    l=list(map(int,input().split()))
    pos=0
    if n==1:
        print(1)
        continue
    maxi=-19900000
    for i in range(0,n):
        if l[i]>maxi:
            if i==0:
                if l[i]!=l[i+1]:
                   pos=i
                   maxi=l[i]
            elif i==n-1:
                if l[i]!=l[i-1]:
                    pos=i
                    maxi=l[i]
            else:
                if l[i]!=l[i-1] or l[i]!=l[i+1]:
                    pos=i
                    maxi=l[i]
                
    if len(set(l))==1:
        print(-1)
        continue
    else:
        print(pos+1)

