Definitely go with a dual band ham antenna covering the VHF-Hi and UHF bands. That will give you best performance on the two bands you're interested in. I like this one (-->
http://www.theantennafarm.com/catalog/diamond-rh77ca-4968.html <--), but make sure you get the correct connector to match your radio. They make the antenna with a BNC (like the one in my link) as well as various SMA versions (like
http://www.theantennafarm.com/catalog/diamond-srh77ca-4983.html and
http://www.theantennafarm.com/catalog/diamond-srj77ca-5210.html) depending on what your specific radio needs.
Although the packaging states "It can additionally receive these bands: 120, 150, 300, 450, 800 and 900 MHz.", don't put too much faith on that. If the signals are strong enough, any antenna will receive any frequency. If you want good performance, use an antenna designed to cover the band or bands you need it to cover. Don't fall for the marketing hype or they'll start saying the antenna will work where it was designed for, where it wasn't designed for, and even claim "It slices!!! It dices!!! It Chops!!! It will even cook your food while you sleep!!!"
The RS 800 MHz antenna works great on that band (the 800 MHz band that is), but not so well on the other ones. I know this because I have several as well as some dual band ham antennas. Using the 800 MHz antenna, I get great coverage on that band, but only pick up the very strong stations in the 150 and 450 MHz bands. Using my dual-band ham antenna, I can pick up even the weak stations on the 150 and 450 MHz bands, but only get the strong signals on the 800 MHz band.
If what works for folks (in special situations) is going to be the guide, than I can claim that no antenna (actually nothing plugged into the antenna jack) works best based on my experience. Now for the details behind that wild (but true) claim. I live about a mile and a half away from a simulcast digital 800 MHz system's tower. With any antenna on my digital scanner, I get poor reception on that system. This is because it's a powerful simulcast system (they have several towers that all broadcast the same information on the same frequencies) and my poor reception is due to picking up multiple towers and having the signals mixing together causing them to distort. When I unplug the antenna, I get the close by tower well enough to get good reception, but no longer pick up the other towers, so distortion due to the signals mixing is no longer a problem. My point is, accept what others say as being true for them, but understand that your results may not be the same.