Some speakers are designed with a lot of power hitting them in mind so they will barely be audible with a standard low power headunit. Those have a low Sensitivity rating, 83 or 84 dB as an example. Other speakers like the Polk DB series are designed to sound good with much lower power levels and they'll have a much higher Sensitivity rating like 90 dB or higher. With a standard car radio or aftermarket head unit without an aux power amplifier, stick with speakers with a 90 dB or higher Sensitivity rating and you should be pretty happy with the results. Again, the Polk DB series of speakers fits right into the high sensitivity rating so they would be among the best choices for a speaker for a Jeep.
Even a great speaker can sound bad if it's not a good match, Sensitivity-rating wise, for the radio or amplifier it is being connected to.