James, I'm no expert and the best advice I can offer is to spend a while on www.k0bg.com;
it's a fantastic guide for newcomers to mobile operating.
I might suggest that you not look for one antenna for all four bands. My car setup has a simple dualband for 2m/440, a bumper mount for HF (20-10), and on a secondary mount right now, a 6m quarterwave. (I don't know why I bother; 6m is rarely open to anywhere when I'm in the car and there is nobody on the local 6m FM repeaters.)
It means more mounts, but using different antennas for HF and VHF/UHF will give you a lot more flexibility in what antennas you can use .... JMHO, of course, YMMV.
Good luck and 73! --ken ac4rd