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. 

I hate to say it, but some of the newer machines just don't facilitate top-stitching very well. 

I got the best results after investing in the Singer Heavy-Duty 4452. I only use it for denim and leather projects. Buying a new machine shouldn't be the fix, but for me it was.

In hindsight, I may have invested instead in tools, such as a walking foot and clearance plate. Those really made a difference------they were included with the Heavy Duty Singer, but they can purchased separately for most any machine.

I understand how aggravating it can be. The same thing happened to me.

I hate to say it, but some of the newer machines aren't very good at top-stitching.

After purchasing the Singer Heavy-Duty 4452, I was able to achieve the best results. I only use it for projects involving denim and leather. Buying a new machine should not be the solution, but it was for me.

In retrospect, I should have spent the money on tools like a walking foot and clearance plate. Those made a huge difference—-they came with the Heavy Duty Singer, but you can get them separately for almost any machine.