Am intending to save some money and top up with a loan later in the year or next year so as to buy a plot which in future i will build my home.

Between building a house or rather, a home, on a 50 by 100 plot within a fairly opened up area with lots of people around building (an area like Utawala) and building a home quite far away from the opened up area where basic commodities are available but its not remote (an area like Ruai, KBC or Joska) on half an acre.

Assuming the two parcels cost the same, which would make a better home?

Places like Ruai, Joska et al. that are less densely populated now will be as densely populated as Utawala in just a few years. You are better of buying the larger place because you and your family will have lots of flexibility interns of what you can do with a bigger plot.