It's not the material that matters, it's the configuration. You can certainly use braid for a fly sparge setup if you configure it correctly.Others may disagree but my understanding is that for fly sparging a false bottom will give better results. If you are batch sparging, I believe that equal results can be obtained from either method.
Sorry to contradict you, but I had no problems getting 5.25 gallons of 1.075 wort with a 5 gallon cooler.as far as 5 gallon cooler vs. 10 gallon cooler - I would point you in the direction of a 10 gallon cooler.
The reason is that you can only mash up to about 1.060 grain bill for a 5 gallon batch in a 5 gallon cooler.
If you ever want to increase your yield, or increase your SG, you're stuck if you buy the 5 gallon cooler.