I think you mean best deal to worst deal, but I'll infer!

Let's say the small size has 100 gallons of detergent (I know right?!), and costs 100 dollars.

Then medium costs 150 dollars and has 80 gallons of detergent.

It should, to be a fair deal, cost 150 dollars with 150 gallons.

Obviously medium is worse than small.

M

where < means worse.

Large has 200 gallons of detergent, and costs 195 dollars!

It should cost, to be a fair deal, 200 dollars!

It is 5 dollars cheaper!

Therefore, Large, Small, Medium from best to worst. Unless the detergent has short shelf life...