which one is better nano aurdino or transistor? Answered

https://mg.mail.yahoo.com/neo/launch?.rand=eddukd0...

Here is a kit mouse line follower for $23

Here is a minimal circuit Line Follower and how it works.

Click the pic to view the entire image.

If you just want to build a line following robot, transistor or op amp is cheaper.

If in the future you want to expand on the robots abilities Arduino is better.

https://diyhacking.com/make-line-follower-robot/

Start simple and work on building skills and knowledge. Build relatively simple and slow robots until you know how to make then faster.

Then why not start with one of the documented Instructables to the right?
With no clue about it I fail to see what do you expect - certainly not that someone writes you build instructions and the code?