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 tt in range(int(input())):
    n=int(input())
    l=list(map(int,input().split()))
    m=max(l)
    b=False
    for i in range(n):
        if i==0:
            if l[i]==m and l[i+1]!=m:
                print(1)
                b=True
                break
        elif i==n-1:
            if l[i]==m and l[i-1]!=m:
                print(n)
                b=True
                break
        else:
            if l[i]==m and (l[i-1]!=m or l[i+1]!=m):
                print(i+1)
                b=True
                break
    if not b:
        print(-1)
            
                
                        
                    
                    
