If you want a little puffiness, I like Hobbs 80/20. If you prefer all cotton, I hear Quilter's Dream Request weight is really nice (needlepunched cotton, but no scrim). For hand quilting, I stay away from battings that are needlepunched through scrim (such as Warm 'n' Natural), as the scrim adds an extra layer of resistance.
My favorite machine batting is Mountain Mist 100% blue ribbon cotton, but I find it difficult to hand quilt. Gives a lovely antique look, because this is actually the type of batting that was used generations ago, but it makes my fingers really sore.