I can't offer an opinion on the weights of various battings, but I can offer some thoughts on the eventual appearance of the quilt after it is washed ...decide if you like, or do NOT like, the "crinkly" look. I do not like it, although lots of people do.
I bought small packages of about 8 different bats, and did sample sandwiches of roughly a fat quarter each. This also gave me a whole lot of chances to practice my free motion technique, and also binding methods. I am still working on these sandwiches, but I have learned that cotton batting (both 100% cotton and cotton/poly blends) crinkle way too much for my taste.
I am currently working on sandwiches by Quilter's Dream...one is the recycled plastic bottle version ("Green" I think it is called) and another is with their puffiest polyester, ("Puff"). Both are supposed to shrink and crinkle very, very, little if at all. We shall see!
These sandwiches are also giving me the chance to experiment with all the fancy stitches on my machine and also different threads, including 12 weight thread, which I really like. The whole experimentation process has been very informative, educational, and freeing. I have "allowed" myself to risk making mistakes, which I would never have done on a real quilt top. I have learned enough to realize that I am now aware of some things that would have probably caused big headaches down the road.
The tricky part is keeping track of which batting I have used in each. I started out with written notes, but quickly switched to using the built in alphabet on my machine to actually write the name of the batting into each sandwich. Eventually I suspect they will all end up as cat beds.