I would also say the Crown Vic. A lot of the cops around here drive motorcycles but I prefer the CVPI. It's pretty spooky to have one behind you especially at night because I can just recognize the headlights of the Crown Vic even when its pitch black outside.
Hmmmm, a laptop isn't the best thing to run GTAIV on. GTAIV demands a lot of CPU power. I think that cpu you have is only a dual core. I have a Toshiba laptop myself and i know it struggles to run any games, even Minecraft LOL. The best thing you could do is build yourself a decent desktop computer if you can afford it. I wouldn't go out and buy one because you can save money by building your own. If not then I would uninstall GTA and install a fresh copy. Make a backup of the fresh install just in case something goes wrong. Then start tinkering with the graphics settings starting with the lowest settings possible and no mods. If you find the right settings then you can start adding mods one by one and testing them. All computers are different so it might be just one setting that needs to be adjusted or maybe all. You could also buy a better laptop.