Audio Research LS15 vs. SP14

I’m not sure about the production date for these preamps but they seem to be within the same price range in the used market, basically within a $1200-$1500. All things being equal, which one do you folks prefer in terms of sound quality. I’ll be using it just as a basic preamp with an SS amp, ML Aerius speakers and a CD player so I don’t need a lot of features, just sound quality. Thanks.

Edited to add Audible Illusions Modulus3 as another option although it's priced somewhat lower than the ARC components referenced.