In terms of wheel size a larger wheel will make a bike more self-stable (i.e. if you push it down a road without a rider on it it will stay upright as long as it travels above a certain speed) due to increased gyroscopic forces. Being self-stable makes the bike less taxing to ride since a self-stable bike requires fewer corrective inputs from the rider.

In reality though, things are a little more complicated since gyroscopic forces are just one component of what makes a bike self-stable. Other elements include the the amount of trail and the centre of mass positions of the frame relative to steerable portion of the bike. Both of these are determined by the geometry of the bike which varies greatly from bike to bike.