Use An Arc Brawler

This allows you to protect both lanes and stand in one place.  This lets you defend later rounds easier.  The best brawlers would be to use dynamite and barely for both of these reasons.  This will allow you to get to later stages and get you more gold.

Straife

Straifing will allow you to dodge the bullets shot by the robots.  This will keep you alive longer and let you pump out more damage.  This will help you out tremendously during the later stages where the robots can one or two shot you.