I use Mantis for the LGM tracker because of the features it affords me that Spray sorely lacks - plus Spray has pretty much stopped being developed. I like mantis because it's really descriptive about bugs, letting you know exactly what they affect, what state of fixingness they are in, if they relate to other bugs, and how crippling they are (or if they're a feature request). Unfortunately, this quantity of information also means that it takes a little bit of time to file a bug, so people who encounter a NullPointerException when clicking a button decide to do whatever they were doing through another route rather than fill out the bug form, or they tell me and then I forget. This is where the wiki/forums can came in handy, because it provides people a quick way to report bugs without having to fill out the form. I don't really consider it a non-consensus, just a second backlog of bugs that have yet to be reported on the mantis because people are too lazy to fill out the forms for them. Every now and then, I'll skim through the list, and if I find something important, I'll fill out a mantis bug for it.
LGM preferences:
* Mantis: Bug goes here.
* Wiki: Can be a good place to quickly post bugs when you can't be assed to fill out the form. Essentially a backlog of bugs that still need to be picked through and transcribed into an actual mantis bug.
* Forum: Great for collaboratively discussing ideas or problems. Find out if something is really a bug, and come up with ideas on how to implement something or how to fix a bug. NOT an actual bug report.
* IRC: Great for bouncing ideas or errors off me to see if it's just user stupidity or a bug. If you know it's a bug, don't put it here. We'll forget. Occasionally, it's really simple, or something relevant to what we're working on, so we'll be able to fix it real quick - but don't count on it. I forget. End of story.
* Spray (when you click the Tracker link at the top of ENIGMA pages): LGM doesn't use this because it is inferior. LGM bugs should be reported elsewhere.
* Email: Yeah, no.
Plugin Preferences:
Since I'm always working on the plugin, if you find a bug with it (which is hard to do, since it's such a stable and small module, but it does happen), the IRC is sufficient. If I can't get to it, it usually gets logged on the Wiki so I don't forget.