The 2nd Atari artwork you posted is much better.
If you want to improve it I would say make the Atari logo bigger and as mahuti suggests try putting the wood grain in rather than the colour gradient.
If not alter the gradient so you have more balance between the brown and black.
As for why the Tron one is cooler it just is lol
The artwork fits better and its more colourful.
The whole point of side art is to draw the eye and the attention of players.
Give it some colour and make it interesting