New cars all have sensors all over them, most of those sensors are Radar, and they are not real concerned about radar detection. Thats why older or cheaper detectors go off constantly. newer or more expensive detectors account for that and can filter that out.
Having a detector slapped on the dash is not the answer, its a whole driving mentality, I drive from Ca. to Az. a lot, I pace other cars by 1/2 mile or so, I'm attentive to aircraft pacing ( lines or markers spaced 1 mile apart) they time you.
using a detector properly is like any other tool, reading up and learning how to be productive with it.
Some have mention forums, Good call, guys on there can teach you driving habits and tricks to your unit.
Also instant on can be seen and avoided by pacing other cars and learning how your unit reacts. I know on the desolate stretch of road i drive if I get a wild errant hit, he is out there.
and 9 out of 10 I will run into him.
Valentine makes great units, I've always had Escort another higher end unit, and they have come out with arrows now also. Part of sticking to a brand is familiarity with how they function.
what ever you do, don't expect to buy it stick it to the dash and avoid tickets, its more than that.
Also a unit with GPS and learning cal be much quieter, you can block out all the known door openers/ speed signs and such in your area.
Just my .02