Who is better Bowser or Eggman

In a fight?

Without weapons/power-ups: Bowser would crush Robotnik, obviously.

With weapons/power-ups: Robotnik would crush Bowser, obviously.

The better character?

The Doctor. Bowser is a very one dimensional character, rarely showing interest in much more than kidnapping Peach. Robotnik's goal to take over the world is a logical one, and his character has more depth.