It really comes down to how many guys you have, and how much you can backline. I was in a 10 piece band, and in the states we used a 15 person passenger van (rented) with a trailer for gear (owned). It's expensive to rent, but for a one off or weekend gig we'd do 3-4 cars (owned), and that adds up too (gas mileage). If we were a 5 piece it would've been so much easier...
I'm in a three-piece and we've been using rented minivans with the back seat out. It's tight, and I've just got a head and 2x10, but the savings in gas and (to a lesser extent) rental make a big difference for us. -E
My band goes out in a Chevy Trailblazer pulling a 4x8 trailer.
Four guys in the band, contents of the trailer
1 ampeg fridge
2 orange 4x12's
2 marshall 4x12's
5 piece drum set with cymbals and hardware case
In the back of the Blazer, guitars, bass, 3 amp heads, cooler full of drinks and road food (if we're doing more than a one-off). It can get cramped on longer trips with duffel bags and pillows, etc, but we make it work.