If you can guarantee it'll be a 2018 Expedition, then I'd go that route. Otherwise, the 2017 is SO dated and the GM versions are a mile better. Much easier to drive, better options, etc. However, I don't think any agency will guarantee a GM/FMC so you're best to book whatever is cheaper.

Also: the Suburban/Yukon XL is comparable to the Expedition L. The standard Expedition is more comparable to the Tahoe/Yukon. The bigger variants will be more suitable for 6 plus luggage. The smaller versions will be tight as there's very limited room behind the 3rd row.