I've never had any luck with wide-band pre-amps as they usually just add even more noise to the received signal!
I usually keep my radio's built in pre-amp switched off and even reduce the RF gain to improve the signal to noise ratio. (Seems counter intuitive but works surprisingly well.)
Most radios have a good front end to filter out-of-band noise but sometimes they can still creep in. In these instances a pre-selector or even a simple external ATU can help out a lot. Look out for pre-amps that have some sort of band selection or tuning method to them as that will be part of the pre-selector circuitry.