I've used Dollar a couple of times, and also National. Found both of them to be fine -- good cars, good pricing structure in general.
Just be aware that the primary role of the counter staff in all American car rental companies is in selling additional insurance. This is quite a hard sell, and is usually commission driven. A lot of it is unnecessary, but you be the judge of what cover you need; far be it from me to advise anyone on the detail of this.