I'd never have a bike with a threadless stem; just an aesthetic preference -- they look ugly to me. I've heard tell that the main reason for them is that one doesn't need to adjust the headset bearings every time bars or stem are changed, or height adjusted. I say no biggie; how often do I do that? Less often than the headset should be cleaned/relubed, anyway.
The litany of "bike shop as the font of ignorance" stories is legion on this forum. Do yourself a big favor and bring your questions here.