I have never had much success with stovetop espresso although I own about 4 variations of the caffetiera - all of them in stainless steel.
A friend gave me a Bialetti for my birthday and I read up on the process of making stovetop at a number of different web sites. The advice had some common points, and and some conflicting ideas so I combined these and with a little trial and error got a great tasting espresso from my new allow friend.
I'm not saying that this is THE way to make a good stovetop - it is more a video about how I used it to make mine. All I can recommend is that if you own one and have been frustrated by it - persist, read and experiment.
Also buy a Bialetti 'cause they are cool!