My experience is that Costco, Sam's, credit union buying services make the process pretty hassle free, will get you a car with all the options you want or don't want if it's on a lot within a few state radius at a competitive price with not much work on your part.
It won't be the best price that could be achieved with person to person haggling but it will be close.
So, which do you want? If you want or like to haggle and put up with sales guys for hours to get the best price then bargain on your own.
If you don't like doing that stuff, which is me, then the buying services work well. We used our credit union for the Denali. I gave them and the costco contact the list of options I wanted, and knew there was one vehicle with all those options available within a 2 state radius. Kicker was the color, metallic blue, extra cost option. The credit union came back within hours with the price and when I could pick it up. The sales guy from the Costco contact took longer and had a higher price.
Now for the interesting things. Costco and the credit union used the SAME EXACT dealer!! credit union through the fleet office, Costco via a floor sales guy.