I consider the SP-14 one of the finest sounding preamp available. I'm of the mind that preamps & phono cartidges are the most audible variables of the electronics - nearly as much as speakers, in a good system. Unfortunately, more often than not, it's very hard to make direct comparisons, that's why there are always so many good used components on the market. I have drawers full of phono cartridges, and shelves of preamps that sound "good", but aren't quite what I'm looking for. I haven't listened to the SP-16, but I like Audio Research, and I like most of what they make (at least that I've heard), if I had an SP-14, I wouldn't be looking any further - it's THAT good.
Funny thing about speakers, preamps, and cartridges though, they all have such an influence on a particular system that no one can really say for sure which is going to be "best"...until you try them. It's time consuming, and expensive, but there's no other way.