The *N*S-10's that can be found for cheap on ebay aren't much better than Bose. The only reason they became the "standard" mix monitors in the '80s is because one particular engineer who cut a couple hit records carried his own pair around to different studios before they were popular. That was what he was accustomed to, they worked for him, everyone else thought there was some magic, ended up getting accustomed to the NS-10s themselves, then all of us who came in to the biz in the early '90s had to put up with the ear fatigue they almost invariably cause until we could afford something better to carry with us from gig to gig.
Much harder to find than NS-10s are the once ubiquitous Auratones. These (roughly) 6" single-driver, paper cone LDF cubes can be found sitting above the meter bridge of many of the best studios in the world. They are quite probably the worst speaker ever designed. Most of us schooled engineers learned early on that if you could make a mix sound good on those POS-es, it would sound OK just about anywhere.
Any half-way decent engineer can mix on just about any speaker if they have some time to learn it. That's why every good engineer carries his/her reference CDs all the time, and when they're setting up for a session in an unfamiliar studio, they're playing that material. Not because they want some music to jam to, but so they can learn the speakers.
Monitoring choice is really a matter of personal preference from one engineer to the next and from one speaker to the next. But since nobody but musicians and engineers listen to music in studios (and they're all too poor to buy enough music to move the market anyway) the car or boom-box test is always the most important.
