Model Dillema! Linear/Robust regression games

Hi all! I have a great game, it's called, which model would you pick and why?
You can play FREE RIGHT NOW by viewing the PDF.
Also, what else can you suggest?
The data in question is the relationship between the root collar diameter (diameter at the base of a tree) and the total biomass of the tree! I've included my data here, this subset treats the species "IE".

THANK YOU SO MUCH. Reply with your postal address and cupcake preference ;)