all three, i.e. 19, 20 and 21
where 19 is my aunt's property, who would not sell but only trade for 20
21 is the furthest from water and electricity connection, which would mean the highest development costs and the worst slope location
therefore I tend towards 20, as the view and the land downward are unobstructed and the notary fees eat up part of the development costs (and maybe my aunt could co-finance part of the development, since I enormously increase the value of her property with my construction project and the development)