Hey CD, Welcome to the forum! I am still surprised that the XLR put the rear door where they did on the 27, but many small toy haulers don't even have two doors.
I looked at both the Carbon line and XLR Hyperlite, but looked past the 27s (in both lines) because of two deal breakers that you probably already have considered, but if not you should. One is the sideways bed; the other is the 9 foot garage. Getting in and out of bed from the foot is not easy and can't be done quietly. And, many, many toys won't fit the 9 foot garage.
If these two things are okay with you, and if all things about these units are equal and in good order, I would lean towards the Carbon for the reasons you give: better placed door (again, you still have another door), higher capacity AC and furnace. There could be other factors that could tilt the choice to one or the other.
Another point that might not be important is the exterior height: the Carbon seems taller than it is at 12'3" - XLR is 11'2".... my 29 is actually 10'11". That lower height can help you while traveling or in campgrounds with lots of trees.
My thoughts on the AC. If camping in the south and you actually use the garage to live in you will need a second AC back there, no matter the unit you decide to buy. If you do that, the XLR with its smaller AC would 't be an issue and the lower price could do several things for you , like the second AC, or upgraded mattress (a must do), or tires, or ???
You need to see each one and kick the tires... see if you like one interior over the other. What you mentioned seems like a good price, but I bet there is more wiggle room since it is the off season.
XLR Hyperlite 29HFS
Ram 2500 6.7L CTD
A Modder's work is never done!