I use Thrifty, I always get upgraded. You can go with any reptuable car rental here, you will not have problems. Just get the cheapest.
Reputable companies: Hertz, Thrifty, Avis, Dollar, Enterprise, Alamo, and National.
Beware though, in the US we use the term "car rental", because "car hire" is more commonly associated with a Limousine Service. You don't want that.
