To answer your question more directly:
When I see mic pre's: I see both extreme flatness/clarity/purity as one goal direction, and nice coloration as the other.
(I suppose you could talk about other features - gain, variable impedance, remote mute, polarity, sensitivity, etc. but mainly people want pure sound vs. colored sound.)
They would, of course, weigh the differences to products already on the market, and COST, quality of construction, power supplies, package (rack vs standalone) etc.