Scrim creates a more stable batting (needlepunching through scrim means the batting is needlepunched through a fine layer of mesh), which is why you can quilt it up to 10 inches apart. Warm and Natural is an example of batting needlepunched through scrim. I personally do not like this batting because the drape is stiff compared to other choices. It machine quilts easily, but the scrim makes hand quilting harder than other choices.
I have looked at the Connecting Threads batting sale. A batting that I have used and like for both machine and hand quilting is the Hobbs 80/20. This is a nice batting if you like some loft.
My personal favorite is a 100% cotton batting without scrim (Mountain Mist Blue Ribbon), which is a very traditional batting. This is a flatter batting and the type used in antique quilts. If you have ever handled antique quilts, you may note that they are thin and soft. Because this type of batting is not needle-punched, much less needle-punched through scrim, it needs to be quilted closely (about 2 inches apart). I like it a lot for machine quilting but would never hand quilt it again.
The only type of cotton batting I would consider pre-washing would be one with scrim. You cannot pre-wash the MM Blue Ribbon, for example; it would be much too likely to fall apart.
A newer type of all-cotton batting is needle-punched (but not through scrim). Dream Request is an example of this. It creates a very even all-cotton batting that is easy to both hand and machine quilt. If I wanted to hand quilt an all-cotton batting, this is the type I would get.
A lot depends on the look you are going for. Poly battings don't shrink, so they are often used when a "modern" look is wanted. Higher loft battings provide the more modern "comforter" style effect. Lower loft cotton battings that are not pre-shrunk provide the traditional antique crinkled look.
I'm not sure why one would want to pre-shrink an all-cotton batting. It would be easier to use a low-loft poly, I think. In any case, if you want to pre-shrink a batting it is highly desirable to simply soak it, spin out the excess water, then dry in a dryer. A washing machine agitator will rip a non-needlepunched-through-scrim cotton battings to bits!