Just wanted to chime in here, some very interesting reads!
Best: 1A - Underdog: What can I say, this little bugger is truly remarkable. Consistent, silent, and reliable as solid steel; it handles everything thrown on top of it. Mine have been running solid for 2+ years with daily operation. They look like an etsy-ish wooden oil diffusor (which it does as well) so you can leave it in plain sight. Not to mention the efficiency to vapor ratio is the best I've seen in any vape. The vapor is near perfect, you can't scorch it but I do believe you extract all the goodness from your plant. Two other points, one is the versatility. Want a wooden stem? Sure. Glass one? Yup. GonG adaptor for water pipe? Oh yes. There is so much you can do it's only limited by your imagination. The second point is Dave, the owner/creator of the UDs. What an awesome individual. If you haven't chatted with him you're missing out, he's a true gem.
Best 1B - SSV: I purchased mine in 2006 and the beast still remains! It's been through several moves, some rough usage, and being dropped more times (sliding off a table) than I care to admit. Still works as well as the day I purchased it. Potent! It is nowhere near as efficient as the UD but if you (or 2-4 people) are looking to get rocked, she's a peach. Not once has someone used it and not been stunned at its ass-kicking ability. Smooth as silk too, never had anything but tasty vapor. I've rigged mine several ways but a SSV bubbler and/or whip have been the best. Great product.
Worst Vapir N02: Was not terrible, it provided fairly reliable (when plugged in) operation for about a year of use. It just never tasted especially great it was almost as if it was 'baked' rather than truly vaporized. While it did the job, it was not that efficient as I pretty much needed a full load every time to get decent clouds. Also, the battery life/heating is crappy. In it's time, it was a good option. Now it seems there are many portables that are superior.