The correct way, at least IMO, is the Super-Chuffer, and to generate the 4-chuffs, I obviously like the Chuff-Generator. The magnets and reed switch are a major PITA to get working right, which is why I developed a better alternative.
I may be a tiny bit biased as those are products I developed, but they do a great job. 
I think you'll find that simply tying the smoke motor to the chuff switch will probably not be nearly as satisfactory. The Super-Chuffer will give you better defined chuffing, smoke at idle, and optionally you get the lighting effects. Here's a couple of clips with the Super-Chuffer and Chuff-Generator.
