The best choice would be the Pastafarian because her light bridge fills in the holes in the tunnel, meaning that if you avoid the slow conveyors, you can earn this easily.
If you don't have the Pastafarian, try the Runner or the Lizard. They work well here because of their great maneuverability.
If you have the "Find more boxes in Infinite mode" upgrade, you can get better control by hitting a box, because that does not count as slowing down for the purposes of this achievement. Only touching the backward conveyors will disqualify you from the achievement.
One more thing that will help is to not go over the forward conveyors too much. You need extra maneuverability and speed will reduce that. It's okay to use them - in fact they tell you the best route, but don't use them too much.