Microphones preamps are very difficult to A/B properly because it's nigh on impossible to get a performance replicated exactly. The dudes at Sound On Sound figured out a replicable source: the Disklavier. And then they did a test of preamps.
Wow. The Mackie and the ART Pro MPAII do really well. And those are the cheapest preamps in the bunch.
Listen before looking at the key.
I've been less and less excited by high-end mic preamps. I own a pair of Neve 1272's and... I will use them on guitars but... I don't care that much.
I certainly don't care about A/D converters anymore (and I own a Apogee).