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 i in  range(t):
    n=int(input())
    a=list(map(int,input().split()))
    #print(a)
    f=max(a)
    if a.count(f)==n:
        print(-1)
        continue
    if len(a)==1 or len(a)==2:
        print(a.index(max(a))+1)
        continue
    r=0
    for i in range(len(a)):
        if i==0:
            if a[i]==f:
                if a[i+1]<f:
                    print(i+1)
                    r=1
                    break
        elif i==n-1:
            if a[i]==f:
                if a[i-1]<f:
                   print(i+1)
                   r=1
                   break
        elif a[i]==f:
            #print(a[i-1],a[i+1])
            if a[i-1]<f or a[i+1]<f:
                print(i+1)
                r=1
                break
    if r!=1:
        print(a.index(f))