I used a few antennas before and now I have settled with a RadioShack "CB" Mag Mount.
Details: Antenna I have tried include
a) VHF (with loading coil). Still using it sometimes when my car is still and when I need to do some Radio transmittion (amateur band). However, it bends to much in Highway speed which is first ,ugly, and secondly suffer in receiving
b) An Airband Mag Mount antenna from Watson. It is very good when standing still. However again, bends too much in highway speed as it is a very thin antenna. It comes with a small micro-mag mount.
c) Radio Shack CB Antenna. I picked it up (actually 2) for $5 during a clearance sale. I then cut the antenna to 1/4 wave length of airband. The performance is slightly worse than antenna b) above, however, it can withstand highway speed which make up for its reception strength. For $5, I cannot compain. Too bad that there is no Radio Shack any more in Canada.
For those who are worried that the Mag Mount would fly off, I have not experienced any problem with a mag mount yet. I can probably say the mag mount don't even move at all.