Every station apart from Finsbury Park has platforms which are adjacent to each other, albeit separated by cross passages. The easiest location would be Arnos Grove as all platforms can be readily seen without having to move backwards and forwards. Oakwood offers the same, but will miss out on trains which terminate at Arnos.
As a point of pedantry, you won’t see and northbound and southbound trains - the Picc is officially eastbound and westbound, although some signage still refers to north and south.