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

try:
    for _ in range(int(input())):
        x=int(input())
        a=list(map(int,input().split()))
        b=max(a)
        if x==a.count(b):
            print(-1)
        else:
            for i in range(x):
                if a[i]==b:
                    if i==0 or i==x-1:
                        if i==0:
                            if a[i+1]!=b:
                                print(i+1)
                                break
                        else:
                            if a[i-1]!=b:
                                print(i+1)
                                break
                    else:
                        if a[i+1]!=b or a[i-1]!=b:
                            print(i+1)
                            break
except:
    pass