Aurifil is a 50 wt cotton 2-ply thread. Being 2-ply, it breaks a little easier than the more common 50 wt 3-ply cotton threads. I doubt that there's anything wrong with your Aurifil thread; it's just a little different than what you are used to. If you want a lint-free, fine thread like Aurifil that is 3-ply, try Presencia which is a 60 wt cotton 3-ply thread.
I like Aurifil for piecing because it gives me great accuracy -- better than any other cotton thread I have tried, although Prescencia is probably at least as good. I don't like polyester thread for piecing because it is slippery compared to cotton, meaning if you cut thread ends short, they can actually slip out at the end of the fabric.
I think Aurifil 50wt is plenty strong for piecing, especially since I quilt pretty closely (nothing more than 4" apart, and usually much closer than that). Close quilting relieves stress on the pieced seams, so there is little chance that any of my piecing seams will snap. I prefer polyester thread for quilting because it is stronger and also gives a little "sparkle" to my quilts.