Hi, I'm ready soon to place them into net pot...

Go to a hydroponics store and just get standard round ones. I find they are all for one use only as the roots get that big.

They are all made of plastic of varying sizes and shapes. There is no "Best One". There is what works best for your situation. You can use a 3.5 inch, a 6", a 12" whatever. Their all the same. Just pick one that will work for whatever setup you intend on using.

I believe any of them would work just fine so long as the roots can get through, and all of them seem good to go.