I have owned probably a dozen radar detectors over the years. They have all worked. Now that being said, these days there is more to consider than just the previous XK band models.

The most dangerous type of police radar is Wideband Ka. When they say wideband, that's exactly what they mean. It is over 2.5 Ghz wide. That's a lot of  area and the signal can be anywhere in it. To top it off, this band is also low power to try to cut down your detector's ability to see it in time. Add instant on and you have a VERY formidable combination.

I believe that it is most important to have a detector that covers 100% of the Ka band. That is what you will encounter most, so that is what you need protection from. All other bands (X, K and Laser) are very frequency specific. Most any detector will find these. Many companies will peak up the Ka sensitivity in the middle of the band, where they hope most signals will be transmitted from, but it then tends to fall off toward the ends, dramaticaly in some cases. The better units don't let this happen.

Laser? Be honest. How often do you see a laser? They may be coming into more widespread use and might be more popular in some areas, but for the most part, you just don't encounter it that much. Especially out of town. 

I currently own a Passport (Escort) 8500 and am very satisfied with it. I have picked up K band radar as far away as five miles. The Texas DPS (Highway Patrol/State Police) uses KA and it always gives adequate warning. As good as its been to me though, I am seriously considering a 9500i. Radar technology keeps advancing and so should your detection capabilities.

My recomendations (for what they are worth, I urge you to do some independent research), in no particular order, are the Valentine One, the Passport 8500/9500 and the Bel 985/995. The Valentine seems to have a slight edge in laser detection whereas the Passport does better with Ka band. However they are all good units and you will not be disappointed with any of them. None of these units are exactly cheap, but you get what you pay for. Considering the entire cost of a ticket besides just the fine (time away from the job, increased insurance premiums etc.) spending the extra money and getting a good detector can pay for itself many times over despite the $300-$500 dollar prices.  Also any decent detector will give front and rear protection. Just because it's looking forward doesn't mean it doesn't know what's going on behind.

Just for the record, I do not condone speeding nor do I believe that a radar detector should be used as a license for such. However, with state and local governments appeitite for funds being what it is, they seem to more and more be turning to traffic fines as a way of closing the gap. Radar is virtually uncontestable in traffic court and even if you elect for defensive driving, you are looking at around $100 in court costs. So if Mr. Smokey is going to hit you with radar of whatever type, you should be able to know he's doing it.