Alright guys, there are several choices you can go with, V1 or Beltronics STi or Escort 9500. These three are the top rated radar detector and the best ones you can find. Some people have done a few experiments comparing the sensitivity and accuracy of these 3. You can find a lot of info on
http://www.radardetector.net
All these three have its pros and cons so it really is up to your personal preference. Personally I have a Bel STi and it works pretty well. In the city, even though you get some false alarm (all radar detectors do), it picks up radar signal quite well.
V1 I have never used before but a lot of people like its arrow indicator telling you where the signal is coming from and it also tells you how many sources of threats are present. From the experiments I have read so far, V1 and Bel STi are pretty much the same in terms of accuracy and dependibility.
As for Escort 9500, it has a built in GPS so you can eliminate false alarms. How well it works, I have no idea, you have to find it out on the forum I said above.
When it comes to how far in advance does the radar detector give you warnings, there is not set time or distance. It all depends on your surrounding and amount of traffic. If there are quite a few cars in front of you, your chance of picking up radar signal bouncing off from the other cars is better and vice versa.
All these three have a lot of programmable features and I know both Bel STi and V1 have stealth mode but I am not sure about Escort 9500. What stealth mode is that in area where it is illegal to have radar detector, cops use detector to detect which car has radar detector. With stealth mode, cops won't be able to find out if you have a radar detector or not on your car. It is a pretty awesome feature if you live in a radar-detector-illegal area.
Most importantly, radar detector only detects radar and laser signals, it is useless against laser gun. By the time it picks up the laser signal, the police already have a reading of your vehicle speed. If you want to jam the laser, you need to buy a laser jammer system or blinder or laser interceptor. If you have laser jammer/blinder/laser interceptor installed on you car, police wont be able to get a reading of your vehicle speed.