Choosing parts for a simple obstacle avoider or line follower robot

I could build a chassis from wood - or even better reuse some toy parts - but the focus of this project should be on electronics (sensors, data and programming) and I can't spend much time on mechanical parts. That's why I looked into kits also.

Anyway what about this choice:

  • arduino motor shiled rev3
  • tamiya double gearbox kit (IIRC you can choose ratio when assembling)

Any recommended sensors setup for line following? And for obstacle avoiding? IR or ultrasonic?

Thanks again!