Only one officer to a shift and you have 6 units to choose from? I wish I had that many to choose from while putting in my time at the salt mines years ago! We only had 2 patrol cars for 6 officers, and even though they were identical in make and appearance, we got to pick too, and I obviously used the best one. We were always a single man patrol car per shift. However, during an event or an overlapping shift on Friday and Saturday nights, a couple of officers and both units were on the streets at the same time.
As for the unit I would choose on a shift if I were you, it's no contest, as it would be the Tahoe, hands down. It is newer, bigger (more legroom and creature comfort) and it's a lot more intimidating than a car, especially to those border runners. The second choice would be the white Ford F-150 crewcab pickup, as I like it's stealthiness despite being marked. The third choice would be either of the black and white Crown Vics that is in the best condition. However, I would steer clear of the solid white Vic since the 7 slot rear wheels on it were recalled by Ford several years ago because they were defective and tended to split open. You certainly don't want one to separate while on a pursuit. They were supposed to be replaced at your local dealer with the 12 slot type if you want to check the others and the spare to see if they are also 7 slots. If so, you might want to raise a little stink and see if they can be replaced, but if not, that is an older unit and probably needs to be taken out of service soon. No comments on the Explorer...err, Exploder.