Denim is only an issue when you are going through multiple layers, like sewing on pockets or hemming over seams. Piecing the quilt isn't an issue, quilting it may be (going over seams) but going with a larger size needle usually works as well as getting a jeans needle.
I've not had a slant needle "bounce" off fabric, I have had it where the tip enters the fabric too soon (because of the high seam) and then gets pulled offline as the fabric is still feeding, hits something it shouldn't and then breaks. But then I've had this problem with non-slant needles too, especially if I'm being a bit too helpful and accidentally pull the fabric more than I should. I always sew slowly over the really thick seems to make sure this does not happen.
My older Viking had a "granny gear" for heavy duty sewing - and that could snap even a heavy needle if I got wasn't careful how the fabric was feeding.
I use to sew professionally, along with making almost all of my and my two kids' clothing. From silk lingerie to wedding gowns to heavy snow suits. Even replaced a zipper on an old canvas tent (took the machine out to the lawn for that one), and made a boat cover that could handle highway speeds without coming apart.