In my opinion these two tents are in totally different leagues. Hilleberg is one of the more premium, boutique tent makers out there and their prices reflect that. The REI tent is much more of a every man's tent. Build quality is good and will last for decades if treated well.

Here is a collection of poorly structured thoughts about the different design. The Hilleberg has a MUCH larger vestibule. If you plan to travel in areas with lots of rain where your tent is your only shelter this could be a huge advantage, as you can cook and hang out in the vestibule while it rains outside. The REI will have better ventilation as others have mentioned. This can play a role with condensation build up inside the tent. I used single wall tent on a tour and had to wipe down the inside of the tent every morning before packing due to all the condensation inside. One is a tunnel design and the other is a modified geodesic dome design so it is hard to compare the theoretical strength of the designs. I would speculate the Hilleberg would be the stronger design in high winds and snow build up if properly pitched and guyed. The REI tent will likely be much faster and easier to set up, which isn't just a convenience thing. If it's raining or windy it's really nice to get a tent up quickly so you can dash inside and get dry and/or warm.

I think you need to evaluate how and where you plan to use the tent because I see these are two very different tents for two very different uses. I would consider the Hilleberg if I were in needed of the ultimate, go anywhere, light, bombproof tent for an extended adventure in areas with unpredictable weather, which probably represents like 1% of users. I would consider the REI for everything else.