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 i in range(int(input())):
    n=int(input())
    l=list(map(int,input().split()))
    s=set(l)
    m=max(s)
    if len(s)==1:
        print(-1)
    else:
        ind=l.index(m)
        if ind==0 and l[ind+1]==m:
            for j in range(2,n):
                if l[j]!=m:
                    print(j)
                    break
        else:
            print(ind+1)
    
    
                   
                
    
            
        
        



   
        
        
    
            
                    
        
     
                
    
                  
            
