I travel for work a fair amount and I use an aggregation site, vroomvroomvroom.com
It gives you all the rental car options for the location and the best part is you aren't charged (they don't even ask for credit card info) until you pick up the car. This lets me go back to the site later and if prices have lowered make a new reservation and cancel the first one.
Also, it shows you the total cost so unless you get a GPS or opt-in for insurance you know what your total will be, I haven't had any hidden charges come up.
I'm not affiliated with the site at all, I just use it a lot, it's great.