An Acadia is significantly smaller than a Yukon. A Yukon is a full size SUV, and an Acadia is a crossover. That being said, I have a Yukon and I wish that I had the XL. When we got my SUV, I was going from a smaller one (Pilot) to the Yukon, which is much larger. I was very nervous to go as large as an XL, so that is the main reason we went with the smaller one...as a side note, I don't remember the gas mileage making enough of a difference to even factor in to the decision. For day to day use, the extra cargo room isn't that big of a deal. The only time that I really wish we had the XL is when I grocery shop and on road trips. We have four kids, so the third row is always up, which leaves very little room for suitcases, sports stuff, etc. I would definitely go with the XL- that is what we will be getting next. BTW, I LOVE my Yukon- I'm sure you will too!