I've tried:
Denim needles, topstitching needles
Specialty jeans topstitching thread, Coats all-purpose thread, Coats heavyweight thread, Gutermann decorative thread
Using a normal thread in the bobbin and the heavier thread on the top
Using the same thread both in the bobbin and on top
Adjusting the tension dial
Adjusting the bobbin tension
Doubling up on thread on the top
Using the Janome triple-stitch for a "meatier" stitch look
...but I can't quite get a look I'm consistently happy with.
So, is there a particular combination of things you do that's working for you? I'd love to hear how other people are managing it.