The most difficult part for the charge to follow is the round bulb
Step-by-step explanation:
It is because the power which is dissipated through the round bulb is less and hence more amount of charge must flow through the circuit. If the round bulb filaments are made thicker then it will be easy for the charge to flow within.
The least difficult path for the current or the charge to flow is the connecting wires in which the current is easy to move about and do not require any additional charges or joules heating.