As Todd noted, narrowing down the frequency bands in use at your destination areas would give more accuracy to an antenna recommendation.
One antenna I've had good results with is the
RH789. It's a telescoping antenna, so you can adjust it's link to optimize a specific frequency band. The antenna itself has markings on the side for how must extension is suggested. The RH789 version has a BNC connector, so you'd need to use the SMA to BNC adapter that came with your scanner. However, the antenna is also available with an SMA connection, SRH789. Both are linked on the same
page.
If what you really want is a mobile antenna for your vehicle, you'd need to decide if you wanted a magnetic mount one that can be removed when not needed, or one that uses a mount on the vehicle, usually requiring a hole to be drilled.