I think all the Cullen's cars are awesome.
I saw a new black Mercedes sedan today, and I thought "OMG! Carlisle's car!" The windows weren't tinted though. It suits him (probably because he's a doctor) and it would be something that I would drive.
I've seen silver Volvo S60's around, and since reading the Twilight series I'm in love with them. I've liked Volvos in the first place. I won a grey 1983 Volvo 240 Diesel, which needs new paint (which unfortunately I lack the funds to paint), but I'd totally get it painted silver. I love Volvos.
Rose's car seems pretty awesome. I'm not a BMW person though (although prior to getting my Volvo, I was going to buy a red 1988 M6). This car suits her well.
Alice's Porche seems fast, and the right type of car for her.
I don't think I've ever even seen a Ferrari or Ashton Martin up close before. They seem like really fancy cars though. A Ferrari doesn't scream Bella to me. Her truck matched her personality more. It makes sense why Edward got her the Guardian though.
Lastly, I can see Emmett in his Jeep. I don't like how it doesn't state the model though. I've seen a couple models of older Jeeps which have been made into off-road vehicles. I'm surprised he doesn't drive a massive pick-up though.
These are trucks I could see Emmett in:http://f650pickups.com/page0009.html