a) the pedestrian: does a decent job without too many odd or archaic terms (or uses notes), but loses quite a bit of nuance and detail;
b) overly literal and technical, where it's almost as though you're looking at a palimpsest of the Greek;
c) the rarest, where the translator knows both the source and English very, very well and can capture and convey just about all the detail and nuance.
It's very hard to find anything like (c). What's shocking to me is how easy it is to find sloppy translations. I was looking recently at a translation of Phaedrus where Phaedrus responds to Socrates' initial criticisms of Lysias' speech by stressing its completeness or comprehensiveness. Somehow that slipped by the translator and got turned into something else like just "full," which just blurs up the point being made terribly. What I detected is that the translator was much more careful with Socrates' speeches, which strikes me as sloppy because the whole dialogue was written by Plato, not just Socrates' parts.
The texts lend themselves to complicated, lengthy, sentence structure ample in subordinate clauses, so that a translator interested in holding the interest of a 21st Century common reader may easily indulge in what a more exact translator would call butchery. I wonder how E B. White would deal with this.