wort chiller, Type L or Type M copper?

Hey everyone, so I did a search, and while there was a lot of talk about how to make chillers and how much length, I want to know which type of coil to use.

Mainly I am seeing Type M (cheaper, $40 for 50ft), or Type L (60ft @ $117). Both can come in coil, but I was wondering which is preferable to use as the material for a wort chiller. I know you can use either Type M or Type L, and especially with the price of copper now-a-days, I am using most opt for the Type M refrigeration tubing. I just want to know if there is any drawback or weakness to the Type M tubing compared to the thicker, stiffer Type L tubing, or vise versa.

When you are talking heat transfer you want the thinnest walls possible. Type M wins

You also want it to be easily formed... type M wins

You also want it to be cheap... type M wins

M will work the best or even AC grade copper tubing works too and AC grade is a little cheaper the M i found it for 35 for 50 ft