Jammers and/or detectors are only illegal in CA., OK., MN., VA. and NE. Jammers jam everything in addition to radar. Many companies, such as RMR, sell combination units that do both detecting and jamming. However, nothing will give you any protection against being paced, which is how most highway LEO's will catch you. Many LEO's are equipped with radar detector detectors as well, and [insert supreme being of choice] help you if they catch you with one in any of the aforementioned states. Having said that, many years ago I gave up the practice of trying to gain the the extra hour on road trips by speeding. Now, I pack sandwiches instead of stopping to eat to gain it. Works just as well and I enjoy tremendously low insurance rates as a result of my spotless record, in addition to saving all of the other monies involved.
So, in short, my advice would be to choose neither, obey posted limits, and pack your lunch!