To make a line follower robot which will be better between 2 wheeler and 4 wheeler robot?

Answer 1

using censor scanning ?
seems 2 is legit , it just the balance not good.
so , just make a temporary wheel that 2 only for balance a.k.a 4.

mostly out there are 2 wheel'd :
https://circuitdigest.com/microcontroller-projects/line-follower-robot-using-arduino

Answer 2

Two wheeler robot with a ball caster wheel in the front.