The answer to is:
It depends, it is largely a matter of opinion, and is not static but changing with each update.
Select at least one speedboat like Menace or Legatus, though the latter is harder to get. Pair it with a boss killer, and/or clear screen, and/or a brobot which increases your strength or armor, and/or a brobot with good Perks. Nicola XXS is currently appreciated by a lot of players.
But again – there are no definitive answers. Also different brobots are better for different situations.